I think Nvidia is the way to go. Don't say I'm a Nvidia fan boy either, as I have ATI Radeon 9800 PRO in my PC. I just think that Nvidia now holds the crown for the best performing graphics hardware. The cards also seem to last longer too using existing technology.
ATI also doesn't seem to support the full Direct-X9 c, like Nvidia does.
For example, the new Pixel Shader 3 isn't supported, even in newer ATI cards, and I dont know why... Nvidia uses Direct-X9 c now, even in some of there budget cards (Geforce 6600GT is one of them).
Though Pixel Shader 3 isn't being used in new games yet, it'd be good to have it when they start using it. Basically it allows for more complex shaders to be used, and more of them, pushing the possibilities even more. For instance if you got a card hoping to support the Unreal 3 engine (Though it'd need to be good), you'd have a chance of running it how it was meant to be played.
Both makes are good though, but they just have different ways of rendering games, for instance with shadowing, etc.
To answer the question though, there is nothing out YET, hehe, though i'm sure they are working on it, and a good Geforce 6800 Ultra can push the limits to the x850 standard mostly if some overclocking is used I think.
The new Nvidia cards though with 512mb of memory will push these boundries more, even though they are still based on the 6800 core, and are just being passed on as a 7000 series.
I Hope this helps
