Them motherfuckers have been clocked at 43 mph at a dead run. I don't know where it was at and who was on the timer, but I can damn sure guarantee you they were right on the money. They're fast and can get that way damned quick.
Think about your range, your bullet speed, the wind (always figure in your wind, dammit, can I stress the motherfucking wind enough?) and calculate your lead accordingly.