I can play Crysis on pretty much Very High @1920x1080 - yes my poor 6870 can't handle more :s - and pretty much the same for Crysis Warhead (except Gamer settings instead of V.High).
However when i turn to play MP on C1 or Wars it just laggs like there's no tomorrow! I tried turning everything to "ultra low ugly looking" mode and STILL i get **** FPS....
BTW - C2 runs at about 70FPS for me with my GPU and screen >.>