I guess its all about weight - wind resistance - and hills ,determining your speed. I pulled a jd350 7 an oliver cletrac thru the hills of NW PA.It was working but when we got on the interstate we cruised pretty well. A good work out for the ole 91 Cc with an ATS turbo. On the other hand I pulled a cletrac behind a 30ft goose neck with a 18ft tag along with a JD on it from Chicago to outside of Detroit once. We ran 65 tp 70 and a couple times 75 no problem ,the wind was right the air was cool and the 7.3 was happy. No not a reguler thing - the guys tow vehicle broke its hitch off on a Sunday afternoon so we took him home.