I cant believe you bother checking, little own police whom you allow to download based on the speed they download at.

If your worried they are using up download slots just allow more slots!

Remember that they are most likely only downloading some of that large file from you, probably also getting it from 7 other hosts, it makes it pretty hard to get 3kb a second off every host. (Dunno to many dial up connection that achieve download speeds of 24kb/s, Thats what I used to get with my old 256kb dsl service.)