Its pretty much a wash on the math. you save 400 miles of navigation when you gain 10/mph for 40 hours (a typical navigatin time). This probably costs you 1x extra stops, if you are stopping every 280 miles (=10 stops in 2800 miles). If you are getting 240 you are stopping = 11 times), but you are taking 1 extra hour for that stop. You would have to drive the 400 miles in that one extra hour to make up the difference. At least on my napkin, maybe I am wrong.