I've hit 42 mph & it seems to lose sufficient torque to assist somewhere around 40.
The battery is 1/2 a kilowatt hour & I can get ranges above 40 miles so my "fuel" costs about 6 cents a "tank." It certainly costs more in reality because there's the depreciation on the motor & the charge cycles used to figure the actual cost of a mile from the battery. The battery was over $600 so I figure it's still nearly $1/mile when I hit 700 miles of travel.
I have 3 more range & stamina tests to do:
slight up hill ride for a distance just over 50 miles
steep climb for about 6.5 miles
flat ride to see if I can reach 100 miles before the battery dies.