The successor of the P965, is only slightly faster, with the only difference being support for 45nm CPUs and DDR3 memory. With prices sky-high, DDR3 is not an issue as yet.
ASUS has choosen an AMI BIOS. The overclocking settings are in the same menu and this time it's very user-friendly.
We did of course try 500MHz, which was possible even on some P965 boards, but the sceen remained black. With 492MHz we could see the boot-screen, but booting was impossible. Reducing the FSB to 485MHz, was the maximum stable setting to run some test. This is not that bad, but we expected more.
The board worked up to 1,200MHz without any problems, but we ran into some performance issues that we can't quite explain. The faster the memory setting the slower the results. This may be a bug in the 1.00G version of our board or possibly the BIOS. Meanwhile, ASUS has released a 1.01G version and other reviews doesn't report of such an issue, so we suppose ASUS fixed it in the new revision. Our board did not like to run with 1T setting and even standard PC2-6400U settings with CL5 would not run at 1.80V, we need to increase to 1.90V for stable operation.
While the lower overclocking settings up to 333MHz x 10 didn't cause any problems, we ran into some isses when we used 366MHz x 10. We were disappointed with the P5NT WS board, because we needed to increase the VCore to 1.5375V, but on the P5K it got worse. We needed to increase the Voltage to 1.5500V, because the board would not work stable at lower settings. The VDrop was inside 50mV most of the time, but the sensor resolution of the Winbond chip is only 0.016V, so an exact messurement is impossible. 1.5500V resulted in 1.512V in Everest. The 3,733MHz setting was not possible, as the system wouldn't run stable.
Before benchmarking we checked the reference frequency. At 266.66MHz and 333.33MHz FSB the board was slightly overclocked, so we re-calculated any benchmarks results to "should be" frequencies.