I know it's not the same type of competitive shooter as CS 1.6 and even CS:S, but as a proficient sniper in TF2, my performance dropped significantly when playing in a server over 40-50ms latency. My home server I was in the teens to 20's, so when you factor in how 20ms can affect my performance in sniping, it follows as well that 20-30 FPS could make the difference between a kill and a miss. Nobody could ever see the difference watching me play, but I could feel a difference when shots that were headshots on one server were misses in another.