I cannot resist...............Chuck's maximum 40 foot H3 is actually 41 feet.

Short version of differences apart from the appearance, the H3 is taller with a much higher storage area. The XL has bays lower in height.

From a conversion point of view, the H3 floor height requires a turn in the entry steps and that creates an interior difference in whicyh the XL driver is on the same level as the rest of the coach, and the H3 driver and passenger are usually sitting a little lower than others in the salon of the coach. (Salon is a fancy word for living room.)

Your right foot influences fuel economy to a much greater extent than the height of the coach, but the laws of physics do apply so the H3 could be expected to be a little less economical to run down the highway especially as speeds increase.