Actual TT bikes are pretty fast. When I compare my times on the TT bike to guys who are clearly faster than me in TT's where they are in the 'Cannibal' division (regular road bikes on the same course) I routinely beat guys who I KNOW are faster than I am. I think the TT bike gives you 1.5-2 mph on most course profiles. I think my time on that same course yesterday would be 21-21.5 mph tops on a regular road bicycle.