I came across this from techpowerup:
http://forums.techpowerup.com/showthread.php?t=18473
and using Rivatuner, I was able to get my new BFG 7900GS OC to unlock from 20 pp/7vp to 24pp/8vp.
From a locked o/c speed of 585/1600 to an unlocked o/c speed of 570/1600 (couldn't go higher with the unlock) I got:
500 more 3DMark03 points
300 more 3DMark05 points
200 more 3DMark06 points
96.5 fps vs. 89.9 fps Half Life 2 Lost Coast Video Stress Test
I'm still testing, but I basically got a faster than 7900GT card for $187.99 CAD after rebate with taxes.
From what I read at Techpowerup, it's only the BFG ones that can unlock so far.