I just recently upgraded to an I7 2600k and the z77x-ud5h from an oc'ed q6600. I'm using BIOS F8d. Everything is stable on one of my two Windows 7 64bit Boot drives.
I7 2600k (currently only 40x multiplier while testing)
Cooler Master Hyper 212+
MSI Cyclone GTX 460 1GB
G.Skill RipjawsX 16GB DDR3 1600 (two kits 2x4GB)
Corsair TX 750Watt
Western Digital WD500AAKX
Western Digital WD640AAKS
(Would have got Caviar Black, but money was tight when I bought them
Currently I use two hard drives as Windows 7 64bit boot drives; a Seagate ST3250410AS 250GB SATA 3Gb and a Western Digital WD500AAKX 500GB SATA 6Gb that I was planning to use as an upgrade to my "everyday" Seagate drive. So, until I started using the F8d BIOS, I've had tons of issues with stability and all the problems everyone else has had with the 2600k. There is something I still haven't been able to fix... it's the most baffling problem I have ever had or seen. Using Real Temp 3.70 I have observed my WD500AAKX not allowing the CPU multiplier to go higher than stock 34x, as well as being unable to come out of sleep mode without a BSOD. My Seagate drive has none of these issues with F8d BIOS and both hard drives still work flawlessly on my previous motherboard.
Having tested both hard drives with some games, I clearly saw that with the WD500AAKX I was not getting the CPU overclock I had set in the BIOS. The only settings that were working are voltage and CPU base clock. I have done 2 Clean installs of Windows 7. I've tried everything everyone has written in guides for "proper" overclocking of an i7 2600k and just using auto or normal settings in the BIOS. I put the drive on all the different SATA ports on my board and used a jumper to restrict it to SATA 3Gb; nothing has worked so far and I have no idea what I can do to fix the problem.
Does anyone have any clue why this would be happening?