I was successful in Unlocking my Radeon 6950 to 6970 with just a bios flash! (simpler than it may sound).
My card was a Radeon 6950 2GB XFX HD-695A-CNFC ver 2.
Followed the instructions at:
It did give the the error: Could not erase ROM
So I followed the part that says Run atiwinflash -unlockrom 0
Followed by atiwinflash -f -p 0 bios.bin where bios.bin is the path and filename of the HD 6970 BIOS you downloaded.
I actually didn't think it was this simple but it was, thanks to this site. Remember not all cards can be flashed, but luckily mine was able to be, and many are also. Good luck. I might be able to help if you post a comment.