The most efficient flight will be in slow forward flight , followed I would guess by hovering in ground effect ( which with something with such small rotor diameter is probably 2 inches off the ground ! ) I have found if you fly faster ( anything faster than P mode with collision avoidance on) it does effect battery life badly , but I did expect this to happen , as I was always taught you can't get something for nothing.
And a Ferrari definitely doesn't have better mpg around a track unless you are cruising at 50-60 mph with no one else around , but then who would want a Ferrari anyway.