New i5 Chip Improves Things Considerably: Stable 3.44 Ghz With Stock Cooler

My previous i5-750 processor turned out to be defective. I sent the chip back to NewEgg and got a prompt replacement. The new processor works much better and well within Intel's specs.

With a properly working processor, it is much easier to see the typical i5/i7 behavior when overclocking. It makes an interesting comparison with AMD. Both Intel and AMD processors are unstable when the voltage is too low. This can be anything from a single thread halting with an error under Prime95 to a hard crash. However, at the top, there is a distinctly different behavior. AMD processors tend to become unstable at some temperature threshold and exhibit very similar behavior to undervolting. The variability is the same, you can see one thread halt or the screen turn to multi-colored gibberish or just go black with a hard crash. Intel processors however don't do this. The problem for Intel is thermal throttling when the chip overheats. Unlike AMD, there is no outward sign that anything has happened. The clock drops to a much lower frequency but the chip just keeps chugging along with complete stabillity. However, the fundamental rules are the same: increased clock requires more voltage to remain stable. More voltage means more heat and eventually both types of processor will reach a point when the voltage is not enough to remain stable but more voltage is too hot.

However, Intel's thermal specs are somewhere between cryptic and endecypherable. If my understanding of these specs has improved then the maximum temperature Intel gives would be the center top of the heat spreader (which we have no way to measure without adding our own probe). Secondly, this spec only defines Intel's guarantee for normal operation within the rated wattage. I suppose this might be useful for an OEM but it doesn't help us much for overclocking. The only real temperature we know for certain is when the chip reaches its maximum Tj and thermal throttles. However, the indicated temperatures of when this happens seem to vary from 5 C low for the stock cooler to 30 C or more low with a good third party cooler. Indicated temperature aside though, for all practical purposes, we can use thermal throttling the an upper limit much the same as an AMD error or crash.

What is Stock?
The first question that usually comes up is what a given chip can do at stock settings. However, one needs to be aware that stock is not exactly defined. Suppose we use 1.225 volts VCORE and 1.1 volts IMC as stock. That is fine; I can set both of these manually in the BIOS. So, I save and exit and then re-enter the BIOS. I bring up the Hardware Monitor and find out that the indicated voltage is not what I set. Likewise, I can boot up Windows and check the voltage with CPU-Z. And, I find out that it says something different from both the BIOS setting and BIOS Hardware Monitor. I'm sure one could argue that one of these is more accurate than the other. However, I chose to use the BIOS setting since it is the only thing I can control. What this means is that when I set the BIOS to 1.225 volts this may be a different voltage than what would be available on a different manufacturer's motheboard or even a different model within the same manufacturer. Nor is there any indication that the Auto setting is a common stock value. Perhaps it is most of the time, but I know that my Asus 785 and 79x boards use different stock voltages. Also, what you test with will change the results. Being able to run SuperPi is no real indication of stability. The same system can boot Windows, complete a SuperPi run, and then crash a few minutes or few hours later with no additional stress. My indications are that:

Prime95 Small FFT < Prime95 Large FFT < OCCT Linpack

In other words, I've had settings that passed Prime95 Small FFT but got errors under Large FFT. And, I've had settings that passed Prime95 Large FFT but got errors under OCCT Linpack. However, I've never had the reverse. I've never a setting pass OCCT Linpack but get errors under Prime95 or pass Prime95 Large FFT but get errors under Small FFT. From what I've seen, this relative stress is the same with AMD and Intel. For example, with Prime95 my Phenom II 965 can pass Prime95 Large FFT at 1.4 volts at 3.8 Ghz. However, my Phenom II 965 cannot pass OCCT Linpack at 3.8 Ghz and 1.4 volts. It needs 1.42 volts to be stable. So, I consider OCCT Linpack to be the definitive test. If it can't pass Linpack then I don't consider it to be stable.

What is Stable?
Once you've tested with Linpack and found the point where it passes but increasing clock will either cause thermal throttling with Intel or thermal instability with AMD then where do you go? I have never considered these points to be usable. In other words, I require some margin between where I will run a system and where it has reached its limits. For example, if the system passed Linpack at 180 Mhz x 20 and got errors at 181 Mhz x 20 then I wouldn't run at 180. I would reduce clock two steps and run at 178 Mhz x 20.

We also need some similar margin with Intel's thermal throttling. My preference would be 5 C. In other words, if a given setting passes Linpack without throttling but higher settings do throttle then I would want to reduce clock and voltage enough to drop the temperature 5 C. This should be enough margin to ensure that with changing room temperature, thermal throttling is never an issue. However, this 5 C number can be a problem. If thermal throttling occurs around 95 C then reducing 5 C seems reasonable. However, using a better cooler can drop the indicated throttling temperature down to the 60's. With this situation, dropping 5 C is not the same. The best I could do would be to try to calculate the same ratio. My room temperature is 23 C so if it throttles at 95 C then that is a 72 C range. That is about 14.5x the 5 C reduction. So, I would probably take the new indicated temperature, for example 65 C, and keep the same ratio. 65 C - 23 C = 42. So, I would only reduce 3 C indicated. These margins are the best guestimates I can come up with; if something turns up later to change these then I'll adjust them accordingly, but this is probably a fairly good starting point.

This is the defective i5-750 that I sent back.

And, this is the new one.

I'm going to do the testing in two parts: first with the stock cooler and then with the Freezer 7 Pro. My case has exceptional cooling with its two 200mm fans. So, I decided that to give a more typical result I would unplug the top 200mm fan for the stock testing. With the rear 120mm case fan and front 200mm case fan running, this should be closer to a typical case with three 120mm fans. When I switch to the Freezer 7, I'll plug the top fan back in. I put the side panels back to close up the case (which is how most cases would be). I also decided on a low tech solution to check temperatures inside the case. I have a clock that gives the room temperature but also includes an outside temperature unit. So, I simply set the outside unit on top of the HD 5770 card which is just below the i5 cooling fan.

This is the outside unit setting on top of the video card.

So here the Indoor temperature is room temperature and Outdoor temperature is the temperature inside the case. The screenshot is convenient because it also documents the time and date. However, even with the top fan turned off my case might still be cooler than average.

My case has the vents on top for the top fan.

And, the left side panel is well ventilated.

Aside from the case ventilation there is also the question of CPU fan setting. My BIOS allows setting for a slower, quieter fan or a faster, noisier fan. I decided to leave the setting at Auto since I don't think all BIOS's have this range. We know that at some point, the stock cooler will be inadequate and the highest fan setting might allow just a little more clock but I don't think this distinction is worth testing since the third party cooler is well above this.

My Results So Far
I'll keep adding results here until I reach thermal throttling with the stock cooler. I would guess that thermal throttling probably won't occur until 3.45 - 3.5 Ghz.

1.225 volts VCORE, 1.1 volts IMC BIOS setting
148 Mhz x 20 = 2.96 Ghz - Linpack stable

1.25 volts VCORE, 1.15 volts IMC BIOS setting
168 Mhz x 20 = 3.360 Ghz - Linpack stable

This is a typical screenshot with the 1.25/1.1 volt test at 3.36 Ghz showing the indicated temperature running about 81 C.

And, this is the clock at the same time showing the case at about 16 C above room temperature.

And, this is the screenshot of the completed Linpack test.

My i5-750 completed Linpack at 1.28125 volts VCORE, 1.20 volts IMC at 3.42 Ghz.

And 3.48 Ghz at 1.30625 volts VCORE and 1.25 volts IMC.

And, finally we find the top:

12/17/09 19:04:15 9.000 0.000 9.000 100.00

We've clearly found the ceiling with the stock cooler. At 1.34 volts VCORE, 1.3 volts IMC at 3.56 Ghz everything shows thermal throttling. With the OCCT graph reading 93 C max we will have to bring it down to 88 C to have a 5 C cushion.

And here is the clock shot showing the temperature inside the case about 20 C higher than room temperature.

I have the OCCT temperature graph handy from the previous 3.48 Ghz speed.

However, this graph touches 90 C. So, I had to come down one step to 20 x 173 Mhz = 3.46 Ghz to pass Linpack with 88 C. Next is the issue of stability. Normally I would drop down 2 steps to 171 Mhz while leaving the voltage at 1.30625 VCORE and 1.25 volts IMC to ensure stability. However, I've already established that this voltage is stable for 174 Mhz. So, using this number we drop two steps to 172 Mhz. And, this gives us our official stock cooler testing speed: 20 x 172 Mhz = 3.44 Ghz. This is a 29% overclock with the stock cooler. Not bad at all.

With Turbo turned on, using the stock cooler, the maximum clock is 165 Mhz which gives about the same speed.

Turbo Off : 20 x 173 Mhz = 3.46 Ghz
Turbo On: 21 x 165 Mhz = 3.465 Ghz

Now it's time to reinstall the Freezer 7 Pro.

My Impressions, So Far

I sent my i5-750 processor back to NewEgg last Saturday. I sent it Priority Mail with Insurance and Confirmation. It arrived in Whittier, CA and was accepted by NewEgg yesterday. Hopefully, I'll have a new one in about three days.

Since none of the test data for the i5 was worth anything, I'll just go over my general impressions so far.

Processor and heatsink retention.
AMD processors have pins whereas with Intel the pins are in CPU socket. I prefer the AMD arrangement. An AMD processor should just drop into the socket by gravity. If it doesn't drop in then you probably have a bent pin. I know this well because one of the pins on my PII 965 was bent and I had to straighten it before it would drop in. With the Intel arrangement, half the pins could be bent and you would never know. So, for detecting bent pins, AMD wins.

The second item is the way that the processor is retained in the socket. AMD uses a latching mechanism that grips the pins whereas Intel uses a clamping mechanism that holds the processor down. Here, Intel clearly wins. The clamping mechanism is all metal parts with a metal backing plate; there is no way that this processor is budging. AMD however is a bit worse off. The pin gripping mechanism is not designed to handle pulling loads. Simply put, you must twist the heatsink to break the seal with the processor before you try to remove it. If you just tug on the heatsink, you could end up leaving pins behind in the socket. And, this would almost certainly destroy both processor and motherboard. With Intel, it should be nearly impossible to damage anything no matter how tight the thermal compound is stuck. Be careful with the AMD heatsink and you should be okay but Intel is the clear winner.

Next is the heatsink retention mechanism. I've had both experiences with AMD's. For example, the X3 720 stock heatsink was great; I just put it on and clamped it down. However, the heatsink for the X4 965 was not so nice. The metal loops were too short and I could barely get it on. There was no slack to tighten the clamp. And, you cannot be ham fisted with the clamp because the cam is just made of plastic; I'm sure it will break if you try to force it. The metal loops for the Freezer 64 Pro were just as good as the X3 stock unit; it just went on and clamped into place without any trouble. AMD's mechanism works the same whether it is third party or stock and the retention frame uses a metal plate on the back of the motherboard for extra strength much as Intel does with the CPU clamp.

Intel however seems to have more than one way to hold the heatsink on. The stock unit uses pins that push down through the four holes surrounding the rentention frame. You push opposite diagonals at the same time. I unlocked the pins, then pushed the pins through and twisted the knob on top of each leg to clamp the pin in place. Apparently, however, you can just push the knobs down while in the locked position. This is maybe a tiny bit easier than the way I did it. Either way though, you want to make sure that each knob is down, locked, and the pin firmly attached to the motherboard. The Freezer 7 uses a completely different method. it has a plastic frame that goes around the CPU clamp frame. You have to push plastic pins through the holes in the frame and through the holes in the motherboard. Then you push expander plugs into each pin to keep them from coming loose. This operation is much more than a pain; it is sloppy and includes far too many ways that you could break or damage the plastic parts. I had to push the retaining plugs in (and remove them later) with needle nosed pliars. And, they take a fair amount of force to push in and pull out. I don't know if these are all similar with third party coolers on Intel motherboards but the Freezer 7 requires patience and a fair amount of care before you apply force. Then, once you have the plastic frame mounted you attach the actual heatsink bracket with two screws. You have to remove the fan to have room to insert the screw on that side. And, fiddling with the other screw in the cramped space between the heatsink and rear case fan is also not much fun.

With AMD, as long as you have a third party cooler that uses the stock latching mechanism then the AMD system is much easier to change processors. With Intel, at least with the Freezer 7, the heatsink bracket blocks the CPU clamp so you cannot change processors without first removing the plastic bracket. This is a major pain. Still, most people probably wouldn't be swapping processors very often so it's probably a hassle that one can live with. I think both of the systems can work with a 500 gram cooler but I wouldn't trust either one of them with anything heavier. Both designs have shortcomings which could result in damaged parts if you aren't careful. However, both systems can (and I'm sure they do) work most of the time.

Changing Clock Speed
I've only worked with Asus motherboards. It is interesting though how different the flavor of the BIOS is from AMD to Intel. My 785 board has few options even though my X3 is Black Edition which allows easy overclocking. The BIOS works fairly well with the X3 just in terms of overclocking. There are items that are mislabeled in the BIOS, for example, calling something a clock setting when it is actually a multiplier setting. And, I have to say that I don't understand why the Intel BIOS nicely calculates memory speed based on actual base clock whereas the AMD memory speed always uses a base clock of 200 Mhz for its calculations. Someone is clearly dropping the ball here.

However, with the X4, it was another story; it wasn't until I realized that the BIOS was setting the voltage too high and reduced it that I could get it stable at higher settings. This amounted to a bump of at least 100 Mhz. The 79X board is a different flavor. It has more settings and is a little easier to use. However, it seems to set the default voltage lower than on the 785 board. I couldn't get 3.9 Ghz stable running OCCT Linpack without bumping the voltage to 1.425 (when 1.4 volts is AMD's max for this chip). The 785 BIOS is adequate but, when using the PII 965, I like the 79X BIOS a little better. I would guess that this BIOS is more like that of the older 78FX boards.

The Intel BIOS on my P55 motherboard is a bit more polished. As I've already mentioned it correctly displays memory speed even when you change the base clock from 133 Mhz. The disappointments come more from the processor itself. Since regular Intel processors have a locked multiplier they aren't nearly as easy to overclock as AMD processors. You really have to stretch that base clock setting to hit anything substantial (at least with the i5-750 which only has a base clock of 2.66 Ghz). For example, to hit 3.32 Ghz you have to bump the clock from 133 to 166 Mhz. This wouldn't be so bad if it weren't for memory. For example, with the base clock at 166 Mhz you can set the memory multiplier the same as for 1066 Mhz and it will actually be at 1333 Mhz. Likewise you would hit the same 1333 Mhz speed again with a base clock of 222 Mhz if you set for 800 Mhz. Of course, with a standard multiplier of 20, this would be 4.44 Ghz on the processor which is out of the question. However, since Intel has no problem with reducing the multiplier you could just set this to, say, 16 or 17, and get an accessible processor clock. It does work, just not as well as with Black Edition. Naturally, not all of AMD's processors are Black Edition but Intel has nothing remotely like this below the outrageously priced i7-965. Maybe Intel thinks that Turbo makes up for some of what is lacking but I would rather see unlocked multipliers. Finally, I'll mention the x21 multiplier because I've seen this mentioned in several reviews. My BIOS can be set to a multiplier of 21 but is doesn't work; the highest multiplier you can actually set is 20 (the same as the default).

Overall, AMD seems a little easier because of the unlocked multiplier, but if the Intel chipset and processor are able to tolerate base clocks way over the default 133 Mhz, Intel could still end up the winner. It will be interesting to find out.

The More, The Merrier -- Nine More Tests Showing The Chip Is Indeed Defective

After a suggestion from rge (who was involved with RealTemp), I decided I would try a number of variations on the tests. The results however are all the same as my earlier tests.

I ran tests with a number of variations: with OCCT, both the CPU test (which is basically Prime95) and Linpack (which is similar to Intel's Burn Test). If you have only 4 GB's and use just a fraction of the memory the test will cycle quickly. However, I have 8 GB's and used 90% of the memory so the cycle time is about seven minutes. I ran Prime95 itself both with large and small FFT's. I also ran i7 Turbo logger at the same time. Some of these screenshots are rather large. My desktop is 1920 x 1080 and I used most of it in the later screenshots to capture everything. Again, just click on the pictures to view them full size. I also included the data from the i7 Turbo log. It shows the data, time, three clock multipliers and the percent CPU load.

12/04/09 15:43:10 20.000 0.001 20.000 1.55
Everything here is normal. The i7 Turbo data agrees with the screenshot.

12/04/09 15:46:44 9.000 0.000 9.000 100.00
Here we have throttling with OCCT Linpack. The multipliers have dropped to the minimum value even though we have 100% CPU load.

At 3:43:10pm which is 4 seconds into the test, the i7 Turbo data agrees with the OCCT graph which agrees with the Windows CPU Meter and the live display of i7 Turbo.

Likewise at 3:46:44pm which is 3 minutes 38 seconds into the test, everything shows the same thing: throttling at 100% load.

12/04/09 15:48:20 20.000 0.000 20.000 2.09
Everything normal.

12/04/09 15:51:22 9.000 0.000 9.000 100.00

Throttling with 100% load running OCCT CPU Test.

12/04/09 15:53:04 20.000 0.000 20.000 100.00
Everything normal.

12/04/09 15:54:09 9.000 0.000 9.000 100.00
Thermal throttling with Prime95 running large FFT.

12/04/09 16:06:09 9.000 0.000 9.000 100.00
Some people seem to prefer small FFT; here is Prime95 with small FFT.
And, everything shows throttling.

12/04/09 16:14:44 9.000 0.000 9.000 100.00

Again, everything agrees. Throttling with 100% load.

12/04/09 16:17:42 9.000 0.000 9.000 100.00
And, in the last screenshot everything including the i7 Turbo data agrees: we have thermal throttling.

Bad Chip Test Results

After more testing I've come to the conclusion that I have a bad chip.

These are screenshots from my last test which I think is pretty conclusive. You can click on the images to see the full size.

This is the beginning of the test. Everything is normal here. The voltage and clock frequency are at normal values. This should be an easy test for the i5-750. I also included the Windows CPU Meter, Clock, and Calendar gadgets for extra verification. Note that the CPU meter agrees with OCCT showing both 100% CPU usage and 90% memory usage.

This period is the gap between test cycles. Note that CPU usage has dropped to 25%. Note that this occurs at 10 minutes and 16 seconds into the test.

The most important thing to note here is that the CPU clock has dropped to 1.2 Ghz but CPU activity is still 100%. This is a clear indication of thermal throttling. Note that this occurs at 12 minutes and 19 seconds into the test.

This is the OCCT graph. You can see the large drop at 10 minutes which corresponds to the second screenshot. The smaller dip at 12 minutes is the thermal throttling captured in the third screenshot. You can also see that thermal throttling had been occuring before the 10 minute period between tests.

This chip is definitely bad.

Intel i5-750, Bad Chip Nixes Tests

I don't think these tests were representative; I think the chip is bad.

Below is the original article. I'll have to do a new one after I get the replacement chip.


******************************

I could not get the processor to pass an OCCT Linpack test at 2.9 Ghz. The problem is that the processor heats up quickly to over 72.7 C which is the chip limit. But, when you reduce voltage, the procesor becomes unstable. At 2.9 Ghz the processor gets errors with 1.16 volts. So I tried increasing to 1.18 volts VCORE and cutting the clock down to 2.8 Ghz. The processor is stable at 2.8 Ghz but heats to 75 C. Frankly, I could not get the processor to stay within range higher than 2.66 Ghz with Turbo turned off. I did some screen captures to show this.

The voltage indicated by OCCT on the following images will be slightly less since it drops during testing. When idle, the voltage shows correctly as 1.18 volts.

The maximum temperature for this processor is 72.7 C. With Turbo off, it just stays within the range.

However, with Turbo enabled the processor increases clock and heats up to 77 C which exceeds the maximum temperature. The thing that bothers me is that I'm seeing it exceed its thermal limits with the voltage set at 1.18. With the voltage at the normal 1.25 volts this would be even worse.

We now have our baseline. With the stock cooler, the i5-750 cannot be considered to be overclockable or even within limits with Turbo enabled. This means that the vast majority of people who buy systems with this processor have a marginal configuration at best. Intel pulled the same stunt with its original Kentsfield quads which were also out of range at stock speeds. Anand Lal Shimpi was well aware of this but in true overclocker fashion he simply averted his eyes and pretended it didn't exist. I had hoped the problem had been fixed with the G0 stepping and the lower voltage 45nm Penryns but now we have Nehalem and the problem is back.

There may be some Intel fanatics who will think I'm being unfair to Intel but I tested my X3 720 and PII 965 the same way. The X3 720 is fine with the stock cooler while the PII 965 needs improvement. However, it should be noted that the PII 965 in stock configuration is more than adequate and could even tolerate a mild overclock of maybe 100 or 200 Mhz. So, in stock configuration AMD does what it is supposed to while Intel fails. The next step is to bolt on the heftier Freezer 7 Pro cooler and see what happens.

Intel i5-750, First Look

I now have my Intel i5-750 system up and running. This is the progress so far.

I have three very good processors to compare. I started with a three cored AMD X3 720 in my CoolerMaster Storm Sniper case with an Asus motherboard with AMD 785 chipset and 8 GB's of OCZ AMD gold edition memory (4 x 2 GB's). I never bothered changing to a third party cooler because the stock unit was adequate. I ran it with the integrated graphics which were not too bad but underpowered for games like Dawn of War. The thermal properties of this processor are good enough that I should be able to run it just fine in a small, tighter case with a moderate video card. I have handy a smaller case with neither front nor top fan (only the rear fan) and an HD 4650 video card. However, I do have an upgrade ready for the rear case fan if necessary. I'll probably end up running Linux on this system. The processor is rated at 95 watts TDP.

After the X3 720, I replaced the motherboard with an Asus board with AMD 79X chipset and 8 GB's of OCZ AMD Black Edition memory (4 x 2 GB's). The video was upgraded to an HD 5770 and the processor upgraded to Phenom II X4 965. This processor is the C3 stepping and is rated at 125 watts TDP. I also preferred a third party, Freezer 64 Pro cooler over the stock cooler. The stock cooler, in spite of the copper bottom and heat pipes, still blows hot air down on the board.

I have a second CoolerMaster case, a HAF 922. This has very similar front and top 200mm cooling fans with the same rear 120mm case fan. The box chasis is identical with the same drive bays in front. The power supply is a bit different. This system has a 700 watt CoolerMaster PS compared with the 850 watt Corsair PS in the Sniper case. However, neither power supply contributes to case heating or cooling because they both draw air from the case bottom and exhaust it out the back. My i5-750 is also rated at 95 watts TDP. I suppose the first question people might have is if it draws the same amount of power as the X3 720. No, it doesn't. Even at maxium overclock, the X3 720 barely throws any heat while the PII 965 throws a lot. The i5-750 is in between. It throws a great deal of heat at 3.4 Ghz, much more than the X3 720 does. If I were to make a rough estimate, I'd say the i5-750 must pull around 115 watts. This would put it a little closer to the PII 965 than the X3 720.

I've heard people say over and over that the Intel cooler is poor. It is actually quite a bit better than the stock X3 720 unit which has a smaller fan and no copper core. If the i5-750 really did draw as little power as the X3 720 then the heatsink would barely get warm. But this is not the case. Overclocked to even 3.4 Ghz, the heatsink blows hot air on the motherboard much more like my PII 965 than the X3 720. I'm sure there will be some skeptics who've read some whiz bang review somewhere that claims that is has accurately measured the CPU power draw at some incredibly low figure. Not a chance. The i5-750 undervolted to 1.12 volts still throws more heat at 3.4 Ghz than an X3 720 does at 1.325 volts and the same 3.4 Ghz. The X3 720 and i5-750 are absolutely not in the same thermal class.

So, Intel fudges the numbers? Yes. Does that bother me? No. Keep in mind that I'm not comparing the quad core i5-750 to the X3 720. That wouldn't make any sense because the X3 720 is much cheaper. No, I'm comparing the quad core, i5-750 to the similarly priced, quad core, Phenom II X4 965. The PII 965 is certainly not light on heat and, if the i5-750 can do the same amount of work, it doesn't have to be either. I have a very similar Freezer 7 Pro ready to install so I can at least stop the hot air blowing on the board. I'll add an update after I see how that works. You can see the pictures of the coolers below in my last article.

Note. I haven't switched to the Freezer 7 Pro cooler yet because I'm still trying to establish the baseline with the stock cooler. I have to admit that this is difficult for me. I didn't have any trouble pushing the X3 720 and PII 965 to their limits. And, when I knew what the limits were I accepted them. I ended up with 3.8 Ghz on the PII 965 and 3.4 Ghz on the X3 720. But, I tend to handle the i5-750 with kid gloves. It isn't easy being tough on i5 because doing thermal testing on an Intel Nehalem is like watching an eight year old trying to keep up with teenagers. Simply put, when I started holding the i5-750 to the same standards I used for my AMD processors, the i5 failed. So, I lowered the clock and tried again. I started at 3.6 Ghz then dropped to: 3.5, 3.4, 3.32, 3.154, and 3.078 Ghz without success. I was hoping it would pass at 2.988 Ghz but that just failed with an error. So, I'm trying again at 2.9 Ghz.