Less than that if you're not afraid to put your foot in it.
I drove to Vancouver from my place yesterday. I left at 0300 hours and got there at 0600 hours. And I stopped twice for fuel. Once in town to get enough fuel to make it to the reservation and then I topped off at the reservation.
I left for home at 1045 hours (same route and everything) and got home at 1445 hours.
The difference was I could set the cruise control at 75 and just truck on. On the way home I had to deal with morons in cars and truck drivers who don't have a clue how to drive an 18 wheeler.
That's why if I can I leave early in the morning. Cuts down on the number of retards on the road.