However, on a electric motor and drive, the permenant magnet motors used make peka torque at 0 RPM and there's little change in efficinecy as RPM increases. However, the drive, is most efficient at full load. At part load it uses I beleive pulse width modulation and some waste heat is created switching on/off the circuits. So you want the electric motor at full load, but the IC engine at minimum RPM and throttle and more improtantly, if it's a automatic, it needs to have the torque converter locked up.
Oh... and jsut ot further comlicate matters, engine effciency and fuel economy are not nessesary the same thing. Efficiency would be fuel conmption rate per delivered HP. Fuel economy is fuel consumed per unit of distance traveled. Many engine reach peak efficiency I beileive right at the point where the torque curves begins to taper off.
OH and in reality, the instanataneous fuel consumption of a engine varies much more dramatically. Very lgiht throttle at low RPM's on a small 2.5L 4 cylinger for example is probably around 50mpg, but full throttle near redline is around 8-10mpg. AN IC engien at idle probably only makes about 5-10HP depending on throttle positon, AC and alternator loads. At a highway crusing speed of 65mph @ 2000RPM and part throttle, it's probably around 40HP and at a nice efficient 45mph, its' maybe just 20HP at 1500RPM.