I have a Q6600 CPU with a Dell stock mobo, GTX 480, and 4GB DDR3.
I've benchmarked it and it runs pretty well on Skyrim, Just Cause 2, and Crysis on 1920x1080 and High settings but no or minimal AA and AF. The problem occurs when encountering scenes with plenty of objects, people, etc. I'm guessing this is a CPU or RAM bottleneck. Volumetric effects also cause it some degree of problems, as well as heavy motion blur.
Overall I'm looking for the most cost-effective upgrade for under $200 that I can make, that would enable no problems on Very High settings for all games on 1920x1080, without AA or AF.
I'm either considering an upgrade on the CPU to maybe Core 2 Extreme, or a new mobo that would let me overclock the Q6600. But overclocking would probably mean a new cooling system as well, since these GTX's already run pretty hot.