Re: 49cc vs 66cc
49cc is a joke. The only reason that you should get one is if you are really worried about the law or if you are just going to putt around at a very slow speed. It has zero advantages over the ;arger motor.
I originally had one, as well as a shift kit for my bike. When I rode with other people my shift kit would allow me to take off a little faster, but even with my many gears I couldn't come close to the single speed 66c bikes.