This mod modifies the server side check for if a player moves too far too quickly which then teleports them back. Allows clients to send fast update packets. Beware.
NB: this can also be caused by your server running behind because it can't keep up with 20tps
This allows people to travel faster with things like the IC2 Jetpack.
Just drop it into your server's mods folder and enjoy the freedom. (No harm having it on client, but is not necessary)
Default options allow 10x the vanilla limits which can be increased or reduced.