I'd most recommend the Lifan KP Mini SS3. The most power (13 hp) at 150cc, with a 5-speed. They claim a top speed of 65 mph. Stick a smaller windscreen on it for better aerodynamics, and find out what sprocket combination works best for your needs. Lifan has a dealership network and you can also order it from Venom.
The windscreen that I had in mind is 15" high X 17" wide. Pretty inexpensive too. Various Chinese brands, in clear or smoke.
https://www.amazon.com/Krator-Windsc...cx_mr_hp_atf_m