For the record, my 62mph is not intended to be a slug, rolling roadblock, etc. It's the sweet spot with my particular truck with these particular rail containers. It annoys me to be that slow as well. I can't justify spending the extra fuel to go faster.
If I was pulling flatbed, tanker, RGN, or anything else that isn't a brick I'd be running 70 everywhere because I'd be aerodynamic enough for it not to hurt the wallet so much.