50 mph on a Schwinn Le Tour Luxe on a straight downhill years ago.
Use to do 43 mph downhill on a winding road (35 mph speed limit) on my daily commute until a few JAMs started passing me, then cutting me off. So I started keeping my speed at 35 mph to better manage not crashing when the JAMs do their stupid stuff. So the JAMs desire to race past me has now resulted in them having to go slower most of the time.