Max HP is at near 40% of no load motor speed - max efficiency is near to 80-90% (70-80% usable - typically) of no load speed.
The typical crank drive kit has 3 front chainrings, one for the motor and 2 of differing sizes for pedal power.
With proper size "tuning" the larger chainring is great for efficiency and the smaller for power-torque.


Please note - this graph is based on 100% throttle. Max efficiency is possible at most cruising speeds, more a function of throttle position than rpms.