Who has cycled the quickest 6 mile bike ride?

Depends on the circumstances. Is it something looking pretty much like a stock road bike, or can it be "anything" that's two-wheeled and doesn't have a motor? is it ridden on a track, road? Is it flat or is it downhill? Can the rider have another vehicle ahead acting as a wind shield, or is it an unassisted ride. The record for unassisted, flat-ground, human-powered is something above 100 km/h, but that was set in something looking more like a torpedo on wheels. An ordinary road bike with a decent rider will do around 80km/h in a descent. A top DH MTBer can do well over 100 km/h terrain permitting. Top result for a rider drafting (but not being towed) behind another vehicle is well over 200 km/h, but that's during extreme circumstances.