#85 should in many cases with standard cylinder be a very good choice, and i believe that a guy from a danish forum had been told from Kymco, that it is what they would put in them in taiwan.
Ive got a powerfilter, so it might not be worth anything what i say, but ive tried both #84 and #86, as i couldnt get a #85, and they both worked fine. But i ended up with #84, as it uses a little bit less fuel than the other, when going full throttle.
If you want more speed without changing cylinder, a malossi variator is the way to go
it will get you near 50 MPH if not more