Its a common mis-understood thing.
FPS on your computer is how many frames your grafix card is rendering, this cant be more than your screen is capable of (Most LCD screens these days are either 60/80/100 or 120). If you set your fps_max to 1000, you still wont get more than your screen is capable of, even if it says you are! Its simply not possible!
The server FPS, is in fact a confusing term, as its not actually FPS, it should really be renamed to something like response, as that is what it really means.
So for example a 66 tic server will respond 66 times per second to updated game information from the players, it will ALSO issue 66 game updates to the connected players per second. A 100 tic server would do this at 100 times per second and so on.
The problem is the higher you set the ticrate, the more information the server has to compute and then send and receive this information back to the players.
So if you had a 500 tic server it would be sending so much information that it would be using masses of bandwidth, and since your computer cant possibly respond fast enough or render the updated information, its quite useless in reality.
The trick to good servers and good hit registry is to set both the players and the servers rates to match the ticrate.
Hope you understood