1992 400E, M119 w/ 134K miles
Mileage is spot-on 20 MPG in 50/50 city/hwy driving
High-test fuel
Driven pretty gently by my better half. When I get behind the wheel I am very suspicious of the 268HP factory rating - I think that was very conservative.

1983 300CD, OM617 w/ 255K miles
Mileage is 24.9 MPG in 50/50 city/hwy driving
I drive this one like I stole it. She runs better when pushed. I don't speed much (just go w/ traffic) but I do accelerate as hard as possible.

With Diesel prices higher than premium gasoline in many cases, I question the wisdom of commuting in the 123. But when I drive the 400E "as it was meant to be driven" the mileage drops accordingly.

That said, I was (pleasantly) shocked by the mileage the M119 returned. Makes me wonder why anyone would have bought the 300E back in '92. Then I remembered the price differential when the cars were new....