Attack Speed Reference

Theoretically you can have a (-1) Fastest weapon, which doesn't make sense. There has to be a limit somewhere.

In the past, client hacks could put you to speed 0 or lower, of course they would almost always disconnect you from MS (it doesn't like speeds below Faster(3) + booster being spammed, since no player weapons reach this) but I believe it uses something along the lines of (500ms + speed*45ms) to determine the actual speed, so it's meaningful up to around -12 speed.

The limit to speed 2 may be a new thing, I believe the Wizet Briefcase is already speed 2 so if anything, BW booster should tell you whether that item changes speed at all.