if people's 6950 are breaking after flashing in that thread it's either they using the 6970 bios or pumping way to much voltage though it or letting it get to hot or driver bugs or they don't know what they are doing....http://forums.techpowerup.com/showthread.php?t=138287&page=3
Thats a good read. Might just be scaremongering, but I am not for taking the risk.
using the 6950 unlocked shaders bios is perfectly safe..
my 6950 has been perfectly fine for many weeks now using the 6950 unlocked shaders bios, i game at 930/1450 1.175v

. I would play at a bigger resolution but ATI drivers do not support my CRT gaming screen
.