I think the ATI cards scale well with resolution.
the 9800 GX2 by itself will be the best performing "single card" though.
Though personally I don't really like the implementation of 2 PCB's for it.
a 3870 X2 will run it well, and it's good on power.
Otherwise, 9600 GT's and 3870's are good cards to SLI/crossfire