Last year we drove from Florida to California in 4 days! So, I'm probably the worst person to ask.
In the daylight we stopped to see the sights, (New Orleans, Carlsbad Caverns, Grand Canyon, Sedona Cliffs), and then ate and caught few hours of sleep. From 12:00 a.m. until about 2:00 p.m. I drove as far as possible each day. Coffee in the morning, Mountain Dew all day!
<--- me at about 1:30 p.m. during that trip!!