Too Slow is Dangerous
In graduate school for Transportation Engineering, they taught us that speed differential causes accidents. If everyone on a highway is going almost the same speed, then there are many less accidents. You'll notice semi-trucks are involved in lots of accidents, and also cause accidents. With a 10,000 lb truck, and a 4500 lb trailer, I'm not worried about driving the speed limit. I do get better mileage at 65, but I drive the speed limit on the interstate.
Refuse to buy tires that aren't rated to at least 81mph. eTrailer.com sells Taskmaster tires with that rating. They don't seem to know that, but when you get the tires the rating on the side tells the story. I've read that soon all trailer tires will be rated for 81 mph. About time.