Here's a review made today on the 8800GTS 512MB, its about on par with a GTX when overclocked to 720gpu and 2100mem, it beats the GTX in most games but by a small margin with no AA/AF, with AA/AF they are about on par, this review states that the 8800GTS clocks about the same as a GT, i am sure there are better clockers out there though. So in summary, the GTS is a great card if you are after an upgrade from anything but a GTX or GT.
http://www.techspot.com/review/79-geforce-8800-gts-512/
Anyone else notice the remarkable resemblance to the legionhardware results?