Your cpu is fine (core 2 duo @ 3 GHz) and 8800 GTS 640MB 320-bit still rocks and gives good fps at almost all games. Maybe you need to buy additional RAM! +2Gb should boost your fps and pc work will be faster in general.
But if you decided to change that 8800 GTS to GTX 460 you won't make mistake!
- GTX 460 WILL WORK in your pc!
- That CPU will not bottleneck your GTX 460! Even if it does a little in some new games so what!? I bet you won't even notice! It's not like you have a Celeron 1,2GHz and a GTX 580...
I say buy that GTX 460 and buy additional 2GB RAM and ENJOY!
How am i sure? Well first, we play the same games, and second we have the same components...