Chimp, you don't get it... You really don't get it..
The 8800 is NOT a typical vid card, but with faster speeds. It's not even comparable to typical vid cards, that have 1 GPU, 1 HS/fan, and 12 pipelines, and 6 shaders. It has LITERALLY over 100 processors on the card (128 for the GTX), any one can process a shader, a material, a whatever!
There is just NO WAY to overclock any other card out there to do this, because they still only have 12 pipelines and 6 shaders. No matter HOW fast they run.
Your AMD overclock analogy doesn't work, either. AMD chips overclock, yes, but not without big heat costs, and Intel chips overclock way way more (for the same price) and at a fraction of the heat (using stock heatsinks). Also, you get any AMD dual core and get a Conroe of the same price, and the conroe overclocks better, cooler, using less juice. So I wouldn't be too fast to rush to the "AMD only" or "ATI only" camps. Nomak's right. Go with what's best, ignore brands for the moment. The 8800 can't be beat until ATI totally forgets everything they ever knew about designing vid cards and starts from the ground up like Nvidia did.
EDIT: For the record I can't afford either card. But you can't say "get this card, overclock it, and it's the same" -- especially since those high-end cards don't overclock, and overheat at load already. Not to mention you fry the card you have to get another.