im not an engineer but i can give you my 2 cents...
I think its all relitive as being in the right gear at the right time + Throttle position.... higher the RPM the more fuel the car uses at a set throtle position...
So... low rpm + low throttle = low gas useage... but that = idle lol
I would say speed limit, without cruse control (it over/under compensates ) and go easy on the throttle... DONT BOOST
hah