Overclocking
For our overclocking tests we push the FSB as high as possible, but please bear in mind that the actual CPU used may hinder the overclock of the motherboard.
To do this we lower our QX9650 CPU's multiplier to its minimum (x6), set the memory speed to the lowest available divider, and increase the appropriate voltages to 10 per cent over reference levels, or as close as we can get with the BIOS options available without going over.
We test for stability using four instances of Prime95, incrementally increasing the FSB clock between runs until failure. We then back the FSB back down until we find the maximum stable limit.
With overclocking, your results may vary from ours. Some examples of a board are liable to overclock to a greater extent than others, and as such the figures given should be taken as a rough guide rather than a definitive or guaranteed limit.
Please also be aware that the Intel DX48BT2, DFI LANPARTY LT X48-TR2 and EVGA nForce 790i Ultra SLI were tested for overclocking at an earlier date. The previous results have been added below to provide a direct comparison with the EVGA nForce 790i SLI FTW.
Intel DX48BT2
Using our test procedures we managed to overclock our QX9650 to 394MHz for an effective 1,576MHz FSB. This is despite our QX9770 running stable at its native 1,600FSB, which leads us to believe that with further tweaking you should be able to achieve a little better. Intel pushing this as an enthusiasts' board for overclocking, however, may be over-reaching.
It has neither the ease of use of an ASUS or Gigabyte board, nor the range of options of the DFI, so even if you're willing to spend a lot of time tweaking away to get a stable overclock, you're likely to look elsewhere.
DFI LANPARTY LT-X48-TR2
Overclocking using the DFI board proved interesting to say the least. DFI provides such a wide array of options for tweaking, it can leave even experienced users a little baffled.
Trying to overclock starting from our saved QX9650 profile and adjusting the settings according to our overclocking procedure resulted in dismal results, refusing to POST when the FSB was raised to even 340MHz. Clearly something was amiss, so starting from optimised defaults we meticulously changed the settings one by one to uncover the root of the problem.
Eventually we traced the problem down to changing memory speeds or timings on the profiles. It seems the ‘auto’ timings are saved as set numbers after the first setup, yet appear simply as auto in the bios. So trying to make adjustments with the 'auto' settings enabled resulted in failure as the auto values were no longer correct for the new speeds or timings. Even setting the memory page to optimised defaults didn't fix the problem, only starting from scratch with optimised defaults and setting the memory to the desired settings before you save for the first time. Hopefully DFI will fix this issue in a future BIOS release.
With the cause of the issue finally divined, we managed to achieve a respectable if unspectacular 444MHz (effective 1,776FSB). With array of options available, fine-tuning may see further gains, but to allow a degree of comparability we try to spend the same amount of time overclocking each board.
EVGA nForce 790i Ultra SLI
EVGA's offering gave us a maximum overclock of 426MHz (effective 1,704FSB).
Following NVIDIA's recommendations to leaving the voltages - except for memory - and everything else except for CPU multiplier to auto, enabled the board to boot into Vista at 450MHz (1,800 QDR) but with substantial instability.
EVGA nForce 790i SLI FTW
EVGA's "For The Win" upgrade provided a healthy overclock achievement of 450MHz (effective 1,800FSB).
However, due to the FSB hole at 1600MHz QDR, we were forced to follow NVIDIA's recommendation and run with everything except for the memory voltage and CPU multiplier set to auto. We were then able to jump straight to 425MHz and ramp up to 450MHz.
Despite its average performance at default settings, there's plenty of headroom for raising the bar. The FTW board overclocks better than all three of our competing solutions, and it's no surprise that it currently holds a few top spots in the FutureMark Hall of Fame.
