OK I own a MSI Lightning gtx 260 core 216 1792 MB(ITS NOT SLI A INGLE CARD WITH 1792MB)superclocked.Now according to the reviews i had seen a year bfore it performed at the level of a stock gtx 280.Now if i upgrade to a gtx 465 will ther be a difference in fps in games like METRO 2033,CRYSIS,WARHEAD coz these are the only demanding games in the market.OTER GAMES MY GTX 260 EASILY PLAYS.
Intel core i7 870
6GB DDR3 RAM
650 W PASU.
Both Crysis Warhead and Metro 2033 have stratospheric system requirements, even at medium resolutions-Merto 2033 is practically uplayable on my rig under DX11, even at lower resolutions for example (although its smooth under DX10).
Probably your best option is to SLI a second GTX260, the only other upgrades that will give a worthwhile boost take you into GTX480/HD5870 terratory.
Game system requirements continue to rise but your existing card should play all of them at at least 1650x1080 at or near to maximum settings.
Upgrading to a DX11 card with XP is a total waste: The newer cards are little faster than your existing one, and will still give you DX9 visuals-DX10/11 cannot be used under XP. If I were you, I'd think about migrating to Win 7 first, at least that way you'll get full value from the existing (DX10) GTX260.