Props and gas mileage

I have read several people post that putting on a lower pitched prop not only gives you more power on the holeshot, but also gives you better gas mileage.

I understand how it gives you a better holeshot, but I thought you'd be running at a higher RPM all day so the gas mileage would be worse. For a given speed, say 23mph, are your RPM's higher or lower with a lower-pitched prop?

my rpms at wot only increased 400 rpm. and now i never need to floor it to get it goin. no matter how much weight, before it took a 1/4 mile stretch with it floored now its almost instantanious.