GPU

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
 
thanks for the info guys, seems to me that a upgrade wont relly be worth a upgrade atm. ? at what point would your cpu become a botttle neck for your gpu, i meen would a 4890 or say a 285 bottle neck my E8500 ? I might need into look into OC ing my cpu maybe if that becomes a problem latter on. my mobo has a program to oc if i get a V8 cpu cooler and use the program is it that easy ? or do i have to mess with the ram also? any help would be grate!!! Thanks