Re: I change my mind about the GTX280
Actually I'd bet it's more due to your RAM limitations on the 9800GTX cards versus the GTX 280. In 3dmark it's not going to touch your ram, where Crysis turned up the way you have it will likely tank because of the 512MB vram.
Also, I don't think a CPU upgrade is going to get you very far. Unless it's to a E8600 or something you can get to 4.0Ghz, it will probably be a moot point.
Far Cry 2 has already shown it likes 4 cores, so for future games you're already sitting pretty well.