Well first of all, if you are looking for specs about the cards, go to a gaming site or
www.nvidia.com and se the cards speed and special enhancements. The GeForce 3 cards have better shadow, reflex, lightning effects and other goodies that will make alot of difference to your game, also they are alot faster and the more memory, the smoother the textures and light calculations will be. You will also have the oppurtunity to play in higher resolutions as well.
GeForce 2 MX card ´lack alot of the special abilities in these areas compaired to the "real" GeForce cards and the higher version, the more goodies.
Definately worth a buy.
I upgraded from a GeF0rce 2 GTS 32 MB card to a GeForce4 TI4200 128 MB card, and it´s a different world I can tell you..