Clock speeds don't mean anything comparing ATI to nvidia cards, especially when they're two totally different generations of cards. The ati 19xx cards are a generation behind the nvidia 8800 cards so if you're going to spend that much money on a vid card, you probably ought to get the nvidia 8800. That will of course all change in about 2-3 months when the next gen ATI cards hit the street, but even then they'll be "merely" the same generation as the nvidia cards (DX 10) so the 8800s will still come out very good on the price/performance once you start looking at cards that cost more than $400.
As for the cpu, I'd personally go for that E6600 core 2 duo right now instead of AMD. Again, that will change in a few months and AMD is talking about a massive speedup in their next gen cpus, but they're not even in the hands of reviewers yet so right now the core 2 duo is the chip to get.
For a top end system build right now, I don't think you can beat a core 2 duo and 8800 for performance per dollar. You can throw an additional thousand bucks into a top end AMD cpu and expensive ATI vid card, and you still won't get the performance you'll get from intel and nvidia. It could all change in a few months but you're buying now, not 6 months from now.
