While we would like to tell you that we were able to push the CPU to a new high, we can't. It would seem that the combination of the 875K and the Radeon HD 5970 will not let you get any more. We could get into Windows even at high BCLKs, but even simple tests would crash the system. We tried everything, but in the end the system would just shut down. First the video would go out, then the system would power off and on.
To see if it was indeed the GPU, we pulled the 5970 out and dropped in an ASUS HD 5870 V2. Unfortunately, we ran into the same exact issue. Then we dropped in the least power hungry GPU we could find and saw the same thing. It really looks like this board just does not have what it takes to overclock the 875K. This is a shame really, as we saw decent clocks from the 661.
I think that if the board had even a couple more power phases, we could get more out of the 875K, but as built we just can't.
As all overclocking results are dependent on the hardware you use, your results may vary. Results of our overclocking tests are included in the performance section with the stock scores.
Important Editor Note: Our maximum overclocking result is the best result we managed in our limited time of testing the motherboard. Due to time constraints we weren't able to tweak the motherboard to the absolute maximum and find the highest possible FSB, as this could take days to find properly. We do however spend at least a few hours overclocking every motherboard to try and find the highest possible overclock in that time frame. You may or may not be able to overclock higher if you spend more time tweaking or as new BIOS updates are released. "Burn-in" time might also come into play if you believe in that.