I thought this would be [more] about payload vs vehicle weight. I posted
about the Xbus in another thread. I've since learned that it weighs 992lb, and has a payload of 1/2 ton and a tow capacity of 2000lb.
As to your question -- it sounds reasonable. A well designed vehicle will accommodate loads and grades and {possibly] appreciate the opportunity to 'stretch it's legs'. Optimal BSFC (in pounds per hour) is prolly at 75% throttle were BSHP lies.