Hi. FPS doesn't depend on network but on maps (some are demending) and things or scripts added on servers. So if you compare some server which is prepared for low PC with server which has many ellements - you will always have the difference.
Try here in CryMP.Net servers like Fair Play - HQ ones and Fair Play - Super FPS/Retro. You will see the difference.
If you play Mesa it also depends on settings. Some servers with Mesa are optimized some not. Sometimes you will get 40 FPS sometimes even 100.
This is why.