[OneWingedShark]

he list is dominated by Volkswagen TDI models, as clean diesels are renown for their excellent highway MPGs.

That's kinda an understatement; I have a 1983 Oldsmobile, Diesel, that gets about 38 MPG highway — and this is a big, heavy car we're talking about.

I have no doubt that (1) adding a turbocharger, (2) dropping the transmission and drive-shaft, in favor of a hydraulic [infinitely-variable-]transmission/power-train would increase it even further.

[BwanaNdege]

Your regular automatic transmission with a lockup torque converter will probably be more efficient than a variable hydraulic one.