You're both part right, part wrong.
There are three 8800GTS models.
8800 GTS 320MB G80
8800 GTS 640MB G80
8800 GTS 512MB G92
They are listed in order of performance, with the lesser card at the top.
The 8800 GTS 512MB is better than the 8800GT / 9800GT. Interestingly, the 8800 GTS 512MB molded into what nVidia called the 9800GTX+, and that was then turned into the GTS 250.