well, we don't really know as the game hasn't been released yet. though it will depend also on the resolution you play. but my best guess is that if you're going to play it at most at 1920x1080 i would say a triple core or quad core and a 5850 or gtx 470.
as basically all articles are saying you won't need a better system to play crysis 2 maxed as long as the pc can play crysis 1 maxed already, so that would be my guess. a 5770 might be able to handle it with lower resolutions but i doubt it will handle it maxed with high, or very high resolutions.