Dunno about the max efficiency, but if you don't want it to dip, don't let me near your car! (I get average to bad efficiency out of all my vehicles - and then they get tested with 10-15% more at the service guys' place - at least the bikes) I don't really drive with a heavy foot all the time, but us the throttle/accelerator to get pretty quick 0-whatever times, shift at high revs, and keep the Honda/Pulsar on the boil
How I envy the 16kmplers....