If you ever drive in the middle of the country you will find roads with a 75MPH speed limit and crusing at 85-90MPH seems like nothing.
The only state I can think of that has a speed limit over 70 is Montana. I lived in West Texas and was a state trooper in that state and there are no roads over 70 as of a few years ago ( I may be uninformed over the last couple of years ) and there are a few roads that are pretty desolate and long like highway 67 from Ft. Stockton to Alpine.