For once, you are right. The X800XT PE does beat the 6800 Ultra in most, games. The problem is, you were one of the FEW lucky people who got one. ATI was getting terrible yields on their X800XT PE's and they are just *now* becoming availale to buy.
So for the top end cards, most people got a 6800Ultra over an X800XT PE which were impossible to get when they came out.
Now, lets look over the midrange cards.
6800GT vs X800Pro. 6800GT kills the X800Pro which only has 12 pipelines to the GT's 16. With PS3.0 support and the 16 pipes, the GT was the card to buy.
So people ended up buying the 6800GT over the X800Pro.
Now lets look at low range cards.
6600GT vs X700 series.
No question about it, 6600GT killed the X700 in almost every benchmark.
So for low range 6600GT beats ATI's X700 series cards.
So for last generation, Nvidia owned ATI in sales. Sure ATI has the single fastest card, they were impossible to get. Also, I have no idea what you are talking about via the 6600gt SLI. You would have to be retarded to do that. 6800GT > 6600GT SLI. Also 6800GT = $350ish now. 6600GT SLI = $360. So I don't know where you got that whole 6600GT SLI crap.
Here is a nice little graph that shows what video cards HardForum users bought. Keep in mind that they are knowlegdable and they know what card is better/available in that pricerange.
