I've been battling with my BFG 6800 Ultra OC since early yesterday and was just about ready to concede that the card was faulty. I was experiencing stuttering and freezing within 10-30 seconds of running just about any game and 3dMark05 was near impossible to complete. This was in addition to battling the power requirements and trying to get it enough juice and the various driver versions.
On a last attempt at resolving the issue before requesting an RMA, I downloaded and applied Coolbit2's registry settings to give me access to the core clock and memory. For those unfamiliar with the proper settings:
6800 Ultra Reference
Core Clock = 400MHz
Memory = 1000MHz
BFG 6800 Ultra OC
Core Clock = 425MHz
Memory = 1100MHz
My settings you ask? The core was set at 454MHz and the memory at 1180MHz. Since I 'underclocked' the defaults, all seems to be well and I'm currently enjoying Far Cry.
Let this thread serve as a potential troubleshooting step for those, like me, read numerous unsuccessful suggestions on other sites (turn off fast writes, try a specific driver, etc). Also, if anyone has any idea why the card would default to above the already OC'd spec, I'd be very interested in hearing this. I find it very disheartening that a $500+ video card would require a registry tweak and manually adjusting speeds in order to get it to function.
So, how has coolbits treated you? I'm just curious as I was going to try and take a stab at it also.