I think the 275 will be around the same performance as the 260 SSC is at it's stock clock. I think the 275 is geared directly at us overclockers because all the reviews I've seen say it's a great overclocker. The other thing is the fact that is has 24 more stream processors. These extra processors really seem to show their muscle with the newer games and especially Crysis.
This is a little off topic but Crysis reminds me of a game released about 11 years ago called Trespasser. Even if your PC was a beast, you'd still get around....I don't know..20 FPS with that game. I think with the current rig I have now I should get at at least 30 FPS...lol. If you're curious.... http://www.gamespot.com/pc/action/trespasser/index.html