No, the 6970 is better purely performance-wise, indisputably. It is, however, possible to unlock the extra cores in the 6950 and turn it into a 6970, so in that sense it could be a better choice to buy.
Logox, you know you can edit your posts? You don't have to triple-post if you forget stuff -.-
Following its single performance, the 6970 is also the best in crossfire. However, your CPU couldn't handle 6950s or 6970s in crossfire, and probably not 2x6870 either.