What the other guys said!
I'll add that the 67cc has more potential, and here's why. Seems to me the 49cc units have the same carb, intake and exhaust, etc as the 67cc. 49 cc thrives on this set-up, as the 67cc is limited by it. So the potential is there to get a better exhaust, clean up the intake, ports, etc......and in reality just a little work on the 67cc makes a HUGE difference. Ghost0 is a larger fellow than myself - our bikes have the same gearing - however I have done essentially nothing to my 67cc, while he has tuned his and added a good pipe. He pulls by me at partial throttle like I am standing still!
Nothing beats cc's (if all else is equal
)