Don't overlook the temperature you're driving in either. Warmer weather will net you increased fuel economy due to less air density (richer mixture) and increased tire pressures resulting in reduced rolling resistance. In a 74hp car, that matters. Add in a better fuel blend and you're talking 3-4mpg easily.

The turbo cars are largely immune to the effects of air density since the charge pressure is regulated by the wastegate, not by atmospheric pressure.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]