So you are comparing an HD6950 that can be unlocked to a stock GTX560Ti? What about if we overclock the Ti card to 950/1000mhz? Let's be fair shall we.
GTX560 Ti 448 is as fast as a GTX570 since almost all the cards come factory preoverclocked, even if by small amounts. GTX570 is as fast as an HD6970 up to 1920x1200.
Either way, HD6950 1/2GB is within
2-3% of the performance of a GTX560 Ti, but of course NV still wins in those key 5 games I listed. The only reason I provided a quick GTX580 vs. HD6970 in SC2 is because I didn't even bother to search for other cards. The performance hit 6970 takes in SC2 with AA is massive. Obviously, you can just force MLAA and solve that problem.
The only advantage HD6950 2GB has is that it has more VRAM for mods and if you want to CF. Otherwise, an overclocked GTX560 Ti is just as good as an GTX570 ~ HD6970 (which is what an unlocked 6950 is).
Regarding GTX560 Ti 448, it
performs well and overclocks better than a GTX570. So certainly one can make an argument for the GTX560 Ti 448 vs. a 6970.
This generation has been extremely close. Neither camp was particularly better than the other except for GTX580 that had no competition. The major distinction is that NV performed better in 4-5 games while AMD doesn't have a lead in any particular game to speak of (at least I am not aware of one game like that). While AMD offered excellent texture fill-rate performance and more VRAM which made its cards more suitable for multi-GPU operation scenarios (HD6950 2GB in CF provided a huge bang for the buck in that respect).