470 is a faster card but why? Why do you want to upgrade. I have a gtx 260 and I can max everything I have at 1920x1080 with my c2d and 4 gigs of ram. I can play crysis with everything on high, with textures on very high (and some other stuff on very high) with 2x aa at 24-30 solid FPS.
If you had an 8800 I would say upgrade. But there is little point in upgrading. Unless your bank account if infinite.