The same logic applied to long trips would have you doing 10 or 20 mph over the limit.
7 hours at 55 mph = 385 miles
7 hours at 75 mph = 525 miles
140 miles difference, on a (for me) short road trip.
I often drive for as long as 14 hours so double those numbers, though my average speed usually works out to between 60 and 70.