The 50cc scooter I had topped out at 35mph. I heard that anything 50cc or under was restricted to 35mph, but at the same time, I’ve seen many 50cc scooters achieve 45-50mph. while speed is desired, torque is really the most important thing, since torque usually equals better acceleration. this is typically achieved by a combo of the engine and transmission used on the scooter. my scooter had the old chain and sprocket attached to a centrifugal clutch which didnt provide enough torque to get me up the many hills I live in and around. the higher end scooters have whats called a cvt transmission, (Continuously variable transmission) which constantly applies the right amount of torque to the wheel, allowing you to get up some steep hills. as for makes, I would recommend vento scooters. they make some nice scooters both in looks and performance..
In some states of Australia, the 50cc scoot is restricted to a top speed of 50km/h which just so happens to be equivalent to 1 km/h per cc. Derestricted, a el cheapo 50cc scoot is capable of 65 km/h quite easily. Then you have the sports models such as the Ludix for example which is capable of 80kmh, more than 1.5 km/h per cc capacity. Then, the almighty Aprillia SR50 that is rumoured to be able to crack the ton, 100 km/h. That’s two km/h per cc capacity.
If you have a motorbike capable of such speeds, that is, 2 kilometres per hour for every cc of capacity then please contact the guiness book of world records and proceed to your nearest salt lake flat.