Our AVERAGE miles per day when nothing inbetween warrants spending much time, is about 350 miles per day. Makes for a nice very comfortable days travel for us. The MAXIMUM we ever did in one 24 hour period was 1200 miles, from Yellowstone Park to Topeka Kansas and involved a lot of 80 MPH plus interstate driving. I don't recommend that kind of stint but it was an emergency situation. YOu can DO whatever you need to do so set your schedule to meet what YOU need and by all means be safe.
Good luck / Skip