Highway miles just flat ARE less stressful for any kind of motor vehicle: engine and transmission are warmed up, rev's are usually steady, the entire powertrain is in what is hopefully it's optimum configuration vis-a-vis torque, hp, and gas mileage...
This is ALL presupposing the vehicle is ACTUALLY being kept in optimum condition: air filter, fuel filter, OIL & OIL FILTER
tire pressure, coolant and brake fluid, etc.
Otherwise,
But, TRUE STORY, there are also those like a gentleman just described in an article last week in the
Dayton Daily News who bought a BioDiesel converted 1986 Mercedes Benz 300SDL with 369K on it for $6,000
, then put a new engine ($15K with installation), a "new interior" for $1K (probably MB-Tex plastic seat covers, eh?) and a $1,500 re-paintjob just SO HE COULD BURN THE VEGETABLE OIL HE GETS FROM THE LOCAL GREASY SPOON for a $ a gallon!
Cheers!