If you look up top there's a member who's gone from a 560 to a 6870 and he said the 6870's are better.
Real world experiences >> review sites
As far as "games being optimized for NVIDIA cards" I don't even see how that matters. If you play a game that runs faster on nV cards because it was optimized for them, the net effect is the game is still running faster.
The 6870 only won 1/14 games in that Xbit review I linked to and none of the synthetics. That's a pretty good indication that the 6870 is the slower card.
I'd agree the two are pretty close in multi GPU, but CF drivers aren't exactly building a good rep lately. I've seen people I thought would rather buy an Xbox than use NVIDIA cards buying SLi lately out of frustration with CF drivers.
Edited by Rollo - 2/21/11 at 10:10am