Would you get better performance out of your GTX 460 768 with a Core i5 or i7? Yes.
Would you get better performance with your current system if you choose a GTX 460 768 instead of a GTS 450? Yes.
So I'd say no. If you have an old school Athlon X2 4200+ or something, sure. But Quad-Core, decent architecture, and alright clock speeds means you're fine. But I would OC that from 2.8GHz to 3.1-3.4 or so. Since most games are still dual-core optimized, you really want to hit at least 3GHz as that's a magic number for CPU dependent games a lot of times.