Where are you getting this information?
Your not going to notice an improvement after 35-40FPS, let alone 100 or more.
With games like Call of Duty and Counter Strike in particular, FPS makes a big difference to the hit registration.
For example, in Counter Strike Source you can get 100 Tick servers, which means that the positions of the players are updated 100 times a second, this also goes for bullet fire.. BUT.. it only updated 100 times a second if you're getting 100 FPS at YOUR end.
In Call of Duty, higher FPS means you can fire certain guns faster and with less recoil, with 125 everything is smooth and hits register properly. It's even better with 250 (which is why he isn't happy with the FPS he's getting), it may look smooth with 30 to 40, but that means player positions and bullets are only being updated 30 to 40 times a second, giving you worse hit registration. Also with a constant 125 FPS, the physics become slightly "weird", allowing you to jump further, at 250 FPS you can jump higher, and at 333 you can get to places you normally can't with 125 or 250 (especially higher places).
Just stuff you pick up about games after playing them for a while.
If you ever load in to a Source server and type in net_graph 3, look at the "Out" bar for tickrate, it matches your FPS. If the server is 100 tick but you aren't getting 100 FPS, you won't be getting the full 100, only what your FPS is.