I randomly came across this post and noticed nobody answered so here goes.
You're probably crashing because the unlock is not stable. Flash your stock bios in and re-install drivers. Make sure to use driversweep after control panel un-install.
Unlocking doesn't do a damn thing anyways.
When you open CCC for the first time after installing the latest drivers (12.1 are the best at the moment) make sure you DO NOT ENABLE OVERDRIVE. You should not need it at all!
Fire up MSI Afterburner and make sure you properly unlocked the CFG file and set overclock to 2.
NOTE: Before even using MSI Afterburner I would run Furmark. You should be getting mid 70's FPS minimum without doing ANYTHING! 52 fps is awful for xfire 6950's, that's how I know your unlock isn't sitting well with the cards.
I run mine at 940/ 1350 all day with OVERDRIVE disabled. You will have to up the voltage though in MSI.