I've had this issue since I purchased my Z68X-UD3H-B3 (6-9 months now?), but recently it's really started to bug me again. I have never been able to get this system stable with my RAM running an XMP @ 1600.
I'm currently running the following:
GA-Z68X-UD3H-B3 w/ F11 (v1.0, not 1.3)
Corsair 4x4 1600 / GSkill 4x4 1600 / Corsair 2x8 1600
All of these kits have passed MemTest86+ but show errors in Windows (BSODs, fail HCI Memtest). They work perfectly fine @ 1333. They also work perfectly fine @ 1600 in my Asus based systems.
I noticed before that when I set XMP that it wants to set VTT to 1.2 but doesn't actually do it. So I set VTT to 1.2 and set all timings manually, yet I still get crashes with all 3 sets of RAM @ 1600. I've wasted the better part of this week troubleshooting this thing and am now looking for other ideas (not giving up and running 1333 though!
What do you all think is wrong?