Only way to get a constant 60FPS in these games is to have a Sandybridge/or something with that CPU Power. Because of a bad game engine these games are very CPU dependant.
I've tested this in Oblivion. Tested using a Q9650@4GHz and a GTX 260 and GTX 570. The Low FPS did not increase going to the GTX 570 from GTX 260. would drop down to 30FPS + in some areas. However, using my Sandybridge I get a constant 60FPS with Vsync on, everywhere in the game. Same rules for Fallout 3 and Fallout New Vegas. Same Game engine.
Q9650@4GHz is about as powerfull as a AMD Phenom II 4.2GHz in games.
The Sandy 2500K will manage a constant 60FPS in these games, even at stock...