like type100 said, in the new fits it shouldnt affect mpg that much going fast thanks to iVTEC, on the manual GDs the key is 65-67mph, max speed and just under VTEC engagement

i always go this speed unless in REALLY in a hurry or all my passengers are yelling at me
GD owners only: i also periodically get on and off the gas lightly to make sure VTEC hadnt engaged itself