Curious, but why? They're not any worse than a Suburban or lots of the other superheavies people drive for no reason except ego. GM powerplant, common drivetrain economies. Ford and Dodge aren't much different. Why drive a V10 around empty 99% of the time?
Face it, even riding an FJR isn't based on rationality. It's a DESIRE. What makes our choices superior to those of others? Fuel economy? Puleeze. We eat tires at a rate the superheavies will never have to suffer. Economy per mile is roughly equivalent.
And no, I don't have a superheavy, but I have an FJR.