For a mere moped, the Rieju RR50 has plenty of zip, once you derestrict it, which should only be done once you're 17. Ahem. Moving on, the RR50 makes the same 8bhp as the RS2 Matrix Rieju, which has a racy fairing to squeeze another few mph from it, but the RR should be capable of 50mph. The RR125 uses the same trailie bike chassis, so it goes very well indeed and makes a useful off-roader.