USAGE FROM MOST TO LEAST IMPORTANT: swtor, movies, diablo 3 (when it comes out,) gta 4,
CURRENT GPU AND POWER SUPPLY: evga 9800 gt akimbo model, 500 watt psu
OTHER RELEVANT SYSTEM SPECS: Athlon II x4 640 3.0 ghz 4gb ram asus m4n68t-m v2
PREFERRED WEBSITE(S) FOR PARTS: newegg.com, amazon, tigerdirect
PARTS PREFERENCES: like evga cards. not sure whether to stay with nvidia or go ati....
CROSSFIRE/sli: no single card only
MONITOR RESOLUTION: 1440x900 is max for monitor have a hp 19'' wide screen
ADDITIONAL COMMENTS: want to get high/ultra performance with better frame rates than the 9800 gt
Please post the exact model of your PSU. If it's a quality 500W PSU, then get an 7850. The Athlon X4 will bottleneck that card, but of course you can keep the card later in your next PC. Overclock is not an option because of the poor motherboard.
BTW the 7850 will crush ANY game at that little resolution, so you will run everything at maximum settings but sometimes in CPU-heavy games the framerate will chop a bit so it may become a little unplayable, because of the relatively slow CPU.
They still sell those 460's? That's a very nice gpu too, it will also tear up games at that resolution and your cpu won't bottleneck it. With the savings from the gpu you could get yourself a nice power supply, like a Seasonic 400-500W or similar from Enermax, CM Silent Pro series, Corsair, XFX and so on.
I think a 6870 would be better for that processor (just a personal opinion). But I think it's OK to have a 560 ti/560 ti 448, especially when you want to change the processor. Just make sure you get a decent power supply from good brands.
Also if you want, you can get the 7850 I gave you before and keep it for the next upgrade. It consume very less power.