Meh, both top of the line cards would have amazing performance, that's no doubt.
It's the things like I said, where ATI has to make 13 some odd cards, and nvidia makes 6 that hold their own agains ATI. ATI does better lines, and able to do AA better, but from I've read concerning shadows going through walls, that makes me think their hardware or drivers suck or something.
I don't even consider the X850XT PE and crap because they made that months after nvidia first released their 6xxx series, so it's technically in it's own class. If nvidia wanted to waste their time and money they'd make a 6850Ultra Blah blah to compete with it, but right now they are letting SLI 'soak in' and whatnot because the cards they already put out way back last summer can more than handle the job.
Saw a picture of the ATI X850 512mb card...nothing special, I mean I wouldn't suspect it to be really just because of extra memory, but yeah...I SAW IT