I thinks about speed
I often blast 300 miles London/Cornwall, trying to keep at 80mph most of the way, it all fast roads (except the first and last 5 miles)
Usual arrival time is gone midnight, and it takes a day to recover
However over the last two summers I have driven over 5,000 miles in large vehicles where the speed is limited to 60mph for one and 80mph for the other, which means actual cruising speed was 50-55mph for one and 65-70mph for the other
Whilst 55mph on a German Autobahn even in a large van is borderline dangerous, it was quite relaxing, but an even bigger vehicle (8m length) at a steady 65-70mph even on a German Autobahn was great, I had no problem driving for hours, night or day