The turbo model should be able to get mid thirties pretty consistently I would think. I had a 92 300d which is slightly larger and heavier but with the same motor and got right around 30 highway consistantly and topped it occasionally.

Final gearing is all that matters. If you have a taller diff but no overdrive you could have a taller final gear ratio than someone with an od transmission.

...how many revolutions of the engine per mile.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.