@slaithe: Thanks for the update when you found a resolution. I've just recently unlocked the shaders on my 6950 2gb (getting ~355mh/s @ 840gpu/1250mem), but I'm weary of flashing straight up to the 6970 bios because I read some other people mentioning the different voltages between the 6950/6970. I'll look into doing something similar after I do more research into it.
Unlocked just the shaders? You find a BIOS for that or did you have to modify your own?
From what I understand, the original reference 6950s were just locked down 6970s, hence the term "unlock."
I haven't had any other difficulties with my "6970" now other than heat considerations since I kept my GTX 285 in so I can do Hybrid PhysX. In addition, and this is an issue with AMD's drivers, I can't watch accelerated vids or game while the 6970 is mining, even if I'm using CUDA off the GTX 285 to accel the vid via CoreAVC. As hackneyed as it is, I have to switch over my DVI cable to my GTX 285 and then everything is fine, as long as I don't have to restart the miner. That requires I switch the DVI back, unless I just need to learn something else. I'm not new to cmd by any means, but the switches/parameters change whenever I move the DVI cable from gpu to gpu.
All in all, I'm happy with my purchase of this Sapphire 6950. I'm a gamer, so bitcoin is more of a side hobby, for now. As it is, the GTX 285 runs most of my games to my liking so I can still game while mining and take mining offline when I want to play something more demanding or better detail (more AA, DX11, etc.)
EDIT: And this all probably means I'll be seeking a refund on the 0.2 BTC I spent to get clocktweak.
EDIT2: Another explanation I've read is the 6970s may have also been locked down to 6950s b/c they were too power hungry/wasteful when clocked up to 6970 speed. No matter for me. I have 1000 watt PSU.