For your CPU the most I'd use is an HD5770. Unless you can get an overclock to 3.6ghz, then an HD5850 is appropriate. I wouldn't bother with the GTX465.
Would my processor support the GTX465 without having to OC and screw with BIOS? Because I don't really think that's possible on a heap like this. Also, I've never owned a GPU in the Radeon series, either.
Also, I was looking at the HD5830..I'm thinking some OC would help that run a bit smoother, but what speed would be necessary? The HD5770 looks more like an attempt to buy me into 2 GPU's with Crossfire when I don't have the money for that.
You will notice a 0 performance increase from a GTX465. Maybe a little. But you're going to be spending $100 more for a card that offers 1% performance increase, sucks 2x as much power (literally), runs much more hot, and is, in general, not a very good card. An HD5770 for $150 will run very cool, and play every game decently at your resolution.
Also, depending on your budget, you could grab an E8400 and an HD5850. But that's $450, so it's up to you.