I finally took the GPS with me to clock the speed on my newest build.
E50 High Torque motor with Tomos top end.
Dellorto 14.12 Carb with 58 jet
Sava tires
16 x 45 gears.
Biturbo exhaust
I achieved 37.4mph on the gps on flat ground and it's four stroking when I hit that speed. I could probably tune her to reach 40, but being a full rigid bike I think 37mph is fast enough.