Hey Nigel,
If you read my other posts here (and all over the Internet!) I've been having problems with the P55M-UD2 and OCZ Platinum 1333 Memory. Seems the video problems are down to drivers, but was getting random freezing which was corrupting files and meant I couldn't really use my computer at all...
At rated speed (7-7-7-20, 1.65V, 1333MHz) it was running Prime95 and OCCT for hours but still randomly freezing. Memtest ran for 12 hours with zero errors. Gigabyte tested their own system with same motherboard and OCZ memory and everything worked fine for them, everything on auto (7-7-7-19, 1.5V, 1333). Memory is on the compatibility list...
I have recently purchased new memory: G.Skill Ripjaw 4GB (2x2GB) DDR3 PC3-12800C7 1600MHz Dual Channel Kit (F3-12800CL7D-4GBRH) and installed it this evening. Loaded optimised defaults then set 7-7-7-24, 2T, everything else on Auto. Motherboard sets speed to 1333 and voltage to 1.5V (measures 1.57V in HWMonitor). Ran for a few hours and no freezing at all! Needs some time but looking good so far!
The ram is obviously specced for those timings at 1600, 1.6V. And I haven't tried running at 1600 yet. I basically overspecced the ram so it would be super stable at 1333. Hopefully 1600 (using XMP) will run fine.
I don't know if this motherboard is very fussy, but seems a lot of people with "good" memory are having compatibility issues. Even those with memory off the compatibility list! Now I have to convince OCZ to RMA my old ram. Perhaps it was from a sub-standard batch that shows up in P55 boards or something??
I lost a month trying to fix it through the BIOS, before getting the new ram.
Chris