If I average 75 mph, the mileage will drop to about 33-35. If I get away from Kansas and go to Colorado, when I get up into the higher elevations, my mileage can get over 60 mpg while averaging 55-60 mph.
Obviously a question from someone who doesn't do much cross country touring.
You are absolutely correct, there are way to many variables here.
My guess is a ratio of about half-way between the 3.15 and 3.37 --- 3.26?
Anyway, the slight change in gear ratio is something you can really feel.
A lot of discussion about fuel mileage must also take into account how you ride (like to wind out at every red light?
), wind speed and direction, speed of bike, fairing or windshield size, weight of rider and passenger, tire pressure (don't forget this important factor in mileage and safety) and mods.
One up on a stock 2005 Road King I've gotten 46 on the highway with no headwind.