Contrary to the belief that we cannot distinguish anything over 30 fps, we can actually see and recognize speeds up to 70+ fps. How can you test this? You can quickly do this with your monitor at home. Set the refresh rate to 60 Hz and stare at it for a while. You can actually see the refreshes and it is very tiring to your eyes. Now if we couldn't see more than 30 fps, why is it that flicker free is considered to be 72 Hz (refreshes per second). You can really tell if the refresh is below 72 by turning your head and looking at the screen through your peripheral vision. You can definitely see the screen refreshes then (due to rods being much more efficient and fast).
Anything over 60 fps is adequate, 72 fps is maximal (anything over that would be overkill). Framerates cannot drop though from that 72 fps, or we will start to see a degradation in the smoothness of the game. Don't get me wrong, it is not bad to play a game at 30 fps, it is fine, but to get the illusion of reality, you really need a frame rate of 72 fps. What this does is saturate the pipeline from your eyes to your visual cortex, just as reality does. As visual quality increases, it really becomes more important to keep frame rates high so we can get the most immersive feel possible. While we still may be several years away from photographic quality in 3D accelerators, it is important to keep the speed up there.
Looks like 3dfx isn't so full of it.