Hi Eva,
Sir Sinclair was definitively a visionair but he didn't know much about biking. The speed you have to make to keep on pedaling while riding full throttle is beyond comfortable. Therefore I fit a 7 gear Shimano in mine as well as a hand throttle. This means that I have the choice how much energy I put in pedaling myself and how much support the engine gives. In 7 th gear I go a full round (the pedal) in ±1.5 sec. Thats really comfy.
To be completely honest, this does not really make the sinclair faster to ride, it is to heavy to put much extra speed into it, but it sure makes you go further with one battery charge.
greetz
Frank