Heheh...another reason not to believe Tom's Hardware. Yeah, something is far off. The 6600GT is schooling the 6800NU at everything. Here's some benchmarks you can actually trust:
http://www.xbitlabs.com/articles/video/display/leadtek-6600gt-pcx_11.html
If you don't believe that site, check out Anand's inital 6600GT article as well, but all the cards in that comparison were AGP versions so I didn't post it. However it's hard to say because at some games, even at that site, the 6600GT is beating the 6800NU even at high AA/AF. Very odd...(though in all of those scenarios both cards yielded less than 45 FPS, not exactly playable). One of the 6600GTs in that article is overclocked unlike the other cards.
Actually the 6800NU in here is AGP so it has a slightly higher memory speed. In any case, a 6800NU will beat a 6600GT, especially at new, shader-intensive games and high levels of Anti-Aliasing/Anisotropic Filtering. The 6600GT manages to pull ahead a little bit in Pure Speed benchmarks because of its much higher clock speed, but the difference is negligible. Right now, there is not much difference between a 6600GT and 6800NU for current games. Come next generation however, the difference between the 6600GT and the 6800NU will get larger because of the 6800's pipelines. Also, its doubled memory will help it at high resolutions (at least one resolution up), and/or bigger textures. Let me tell you, though, that the (at least my) 6800NU (PCI-E) overclocks extremely well. Check my sig for clocks/scores.