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
16 x 45 gears.
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.