[Pierre-Marie Baty]

Actually the only relevant criteria are the number of polygons the card can handle each second, and the availability of such or such special effect directly in the hardware, like fogs, texture mappings and filtering functions. The human eye samples its world 15 times a second ; you could eventually play a game at 20 fps and not notice any lag, or very little.

I remember when I was developing my bots with my old computer (500 MHz), most of the times CS was running at 15-20 fps and it was still playable.