You're not going to get much variety on a motorway unless you experience some serious congestion. If you value that one hour so much, you're more likely to just crack on and sit at 80 in 6th. How much are you going to vary your speed on a well flowing motorway? Drop to 40 and 4th gear on a road that is flowing at 70/80, briefly then speed up again? That'll annoy even the truckers and won't do as much to help your "variance" cause as a varied A and B road journey. Good piston ring seal and avoiding bore glaze is the aim here. 7 VW TDIs in a row and only 1 had any oil use between services, the one that spent the first 700 miles of its life on the motorway, using 2 litres of oil in its first 700 miles and a litre per 1000 miles thereafter.