Lee and Kelly, Where you are traveling and the time of year make a difference as well. If you're in the plains and on a straight stretch, 450 miles is a full day, but many travelers go farther. During the long summer days we have stopped in the early evening because we had a stop planned. There were still several hours of daylight left and after a short rest we wished we had driven a few more hours. Keep in mind the trip is as important as the destination.
On the long trips with several one night stops in a row, we get road weary even on the short mileage days. A second night at the same spot really freshens us up.