Just as a point of reference, when I still lived in San Jose, Jim Kikuchi, Steve Hollingsworth and I drove the two Ghias and Steve's Bug from SJ to Phoenix in 10-1/2 hours. We launched at 4:00 am and reached Grapevine (on I-5) around 7:30. Considering that included Pacheco Pass (152), that's flying. We made Phoenix in 10-1/2 hours including a stop in Banning for chow.
You can bet we all checked our valves the next morning. :P
Max