Upgrade a 260

Hi all, I was wondering how much in fps a 275 or 285 would give over a GTX 260 (not a GTX 260/216) i can play crysis at 1680X1050 on high no AA @ about 23 to 40 fps on the 260, Would i get more stable bottom end fps like 40 to 50 with a 275 ? I also have a xfire mobo if you guys think of a ATI card that would be = to a 275 or 285 Thanks niklas
 
The gtx275 is a bit faster but im not sure if it will give you much of an increase over your gtx260. Before you decide to purchase a new video card have you tried to overclock your card and your cpu?