[Ironhydroxide]

now you got me all thinking mathy and such.

I'm tempted to say there is a "double Peak" in the fuel efficiency of an engine. One where the engine speed is slow enough to counteract the extra use of fuel to keep it at said speed; and another where the engine is "officially" at peak torque, but is detrimented by the higher speed, and therefore more fuel consumption per length of time than a slower engine speed.