66 tick isn't mandatory:
http://didrole.com/tickrate_enabler/
It's just the standard functionality of the game. I don't want to get into an argument here over which tickrate is superior, either.
Either way, when developing this plugin using a listenserver on my own computer, which was running with completely default FPS and tickrate (66), 1.5 (%50 above the weapon-specific maximum ground speed) seemed like a good threshold to me. After releasing the plugin and doing more testing on my clan's server (running at 100 tick, 2000fps), it seemed like 1.5 was too high of a limit. If you read the "Nice Details to Know" section, you can find out how to turn a sort of testing mode on in the plugin to figure out a good threshold. I know I could have included that functionality as a cvar or something, but I didn't.