Speed is dependant on your weight as well as other factors. A 40t sprocket can get me at 38mph. I weigh in at 150 Lbs. and I have port matched the intake and exhaust manifolds, switched to a high quality spark plug (NGK B5HS), wire, and cap. I have also cut the innner tube in the exhaust. Plus I have been using synthetic oil in my mixture at a 36:1 ratio. If you really want speed, you can get the Shifter Kit from Sick Bikes.
Welcome to Sick Bike Parts