Those 700c tires really spin, I'd get some 23 mm Gatorskin tires and really go.
I want to build a steel frame fixie MB now
I ride my 26" MTB coverted MB to and from work.
I have also achieved ridiculous speeds on my Giant road bicycle with a nice 105 hub wheelset, Gatorskins, aluminum frame, without a motor, on the same stretch of downhill road on the way home. That roadie has gone plenty faster than my MB without a motor on that stretch. I'd put money on any 700c bike with even decent wheels smoking a cruiser or mtb build with the same exact motor.