QX6700 is going to be 1200 bucks when it comes out, which I'm sure is way out of your price range. The other quad-cores will also be priced decently high when they come out next year, so if you want Price Per Performance, get a dual-core. However, if you want gaming performance, graphics cards are your best bet.
We can say this about DX10 cards, they will totally dominate (not in a S&M fashion) any game out right now and any graphics cards. Only thing to worry about is the price. Even if no games that support DX10 will be out, these cards should be able to destroy DX9 games. But then again, this is all speculation. I would wait for some preliminary G80 benchmarks to come out, and then decide.
Hope this helps.