On a ten hour drive...with an extra 20 mph average ( 55 versus 75 ) is an extra 200 miles per day.
My actual distance is 925 miles. I normally stop for gas a Nephi, UT. 2nd gas stop at St. George, UT plus 30 min for food/restroom. 3rd stop for gas at Barstow, CA. Final destination San Diego, CA...with 1/2 a tank left. Breaks add under 1 hour end to end. At 55 MPH with no traffic the time would be almost 17 hours of driving. The real route today has 70/75 MPH for 710 of those miles. That 9.5 hours for the 710 miles. The rest is currently posted 65 MPH, thus another 3.3 miles. That's 12.8 hours plus 1 hour for breaks. The real trip works out to 14 - 15 hours most of the time with normal traffic and small variations in service at the restaurant in St. George.