Besides being an nVidia guy, cos ATi drivers are stuck together with tape...
If I were in a doubt about the 2, I`d check the OC3D reviews and see if there`s any valuable tidbits I can find in there.
I know the 8800 get outstanding remarks from lots of peoples, but the Ati card hasn`t been out as long .. so meh.
If Kemp had both cards, seeing his results on 2 identical mobos (with the exception of the gfx obviously), would sway me either way.