I also have an 6950 DCuII 2gb, but I think mine might be locked.
I tried for a while when I got it in November, and I'm trying again.
I've tried the Sapphire BIOS W1zzard provides, as well as some Asus BIOS's and AMD BIOS's. (all 6970's)
All they've ever done is boost my clock/memory...