I disagree, i noticed a big difference between my dual core and quad core rig with the same video card.
But the most important thing is that ALL your components work together. heister has the right idea when he says a expensive quad on a cheap board is not good.
But the board he picked out he has experience with and it's not a bad mobo. This rig will turn out alright.
I still suggest the 9600 GT because i've seen such good reviews for the price. and on clubit, after rebates and shipping it comes out below $170, a good deal for something close to performance of a 8800 gt 512.