Rear Sprocket crossover

I recently bought the SUNL 200GY http://www.sunl.com/SLD-200GY.html (it's even yellow just like the picture) anyway I counted the teeth Front is 17 and rear is 56 tooth running on the fourlane I'm lucky to get 55mph/80kph downhill with the wind to my back and the tach is around the 8-9K range. Any suggestions on what size rear sprocket to go with I'd like to run at least 60-65mph without blowing the engine. :mwink:

EDIT: Nevermind figured it out myself

sounds like you need to change your rear sproket for less teeth i would look at 51 which is standard on sinnis apache and think it is on a qlink 200