I spent many years on bikes, racers and mountain bikes going back and forth to school and college. Its the same route i commute now too so you can imagine how much i love just twisting the throttle as opposed to breaking a serious sweat.
Anyhoo, on my racer i could do over 20mph on flat roads and well over 30/35mph downhill on dual carriageway sections.
I crahsed into the back of a police car once

but thankfull they werent hurt