I don't know where you get your information Mike but my CL160 would do just under 70 mph with one rider and about 60 with two. The mileage didn't change that much between one and two riders. The only difference would be wind resistance and if the second rider stayed behind the driver, that would be minimized.
As for mountains, there aren't any in the Indianapolis, Indiana area so I don't know what kind of mileage it would have gotten going up the side of a mountain. You said that no motorcycle with two riders would get 45 mpg, I'm just pointing out that you're wrong because I used to have one that did better than that. But if you're going to change your statement to mean only mileage going up-hill, okay you might be right.
Jack