Ok so they have stated that Fermi isnt as fast as a 5970. Ok the 5970 is 2 5850's in Xfire. So at most you could put 2 5970s in Xfire. However one could theorize 4 Fermis in Quad SLI, which could prove to be faster.

I know the down side would be that 4 cards would suck 1200W of juice, and the cost would be astronomical.

However I would install a Fermi over a 5870 or a 5970, due to driver issues.

I'm not a fanboy one way or the other...Love ATI cards, hate the drivers. Love Nvidia drivers, hate the card cost...