nVidia = Generic. nVidia already make the cards int he first place, eVGA just warranty them and sometimes use a new cooler.
The 320 MB version is the 8800GTS. Currently the 8800GT is faster than the 8800GTS (confusing, i know!), however a new 8800GTS is in the works.
I've never been keen on the 320 MB GTS myself, as i was sucked into buying a low-memory card (256 MB 7950GT, rather than the "full fat" 512 MB version), and with the way textures are going, you will be limited in newer games if you get a monitor over 22".