Having looked at the reviews of the HD6950 and HD6970 performance looks all over the place IMHO. The HD6970 sometimes is much faster than a GTX570 and other times around the same speed as an HD5870.
However,it is interesting to see that the cards seem to do quite well in 2560X1920 and in some newer games too. Crossfire performance looks quite good too.
This means that the architecture will probably do better in newer games. It will be interesting to see if future driver updates increase performance a lot.
Supposedly AMD are going to be releasing weekly updates or something along those lines.
The HD6950 does look quite an interesting card if it drops to around £200 or less. I personally think that AMD should have launched a 1GB version under £200 TBH.