Agree with Whitey; highway miles are easy on the car, and only the driver’s endurance wlimits how far you can drive.
Some years ago our family did a 7000 mile holiday trip in 3 weeks in a Buick station wagon, and often averaged 800 miles a day across the plains. If you observe the speed limits, such driving is good for the car, unless you are overloaded.
The world record for continuous fast driving was a Packard experiment where they averaged 100 mph for 100,000 miles around the factory test track! These cars had their oil changed and fluids checked when they changed drivers. All this in the mid 1950s! Engines were claimed to have no excessive wear athe the end of the trip.