ATi/nVidia equivalents?

[gamepad]

i'm in the market for a new pci video card but i'm really confused about what ATi card matches what nVidia card.

if we can get a list going here or something that'd be great.

 

[monster64]

6800 =x800/pro
6800 GT =x800 XL/XT
6800 Ultra = x800 XT PE/x850 XT
x850 XT PE =<7800 GT
7800 GTX>all

EDIT: oh, and for SLI:
6600 GT x2 =< 6800GT
6800 x2 = 6800 GT
6800 GT/Ultra x2 = 7800 GT/X

 

[gamepad]

thanks