My point of reference is the 91 300SE and 94 S420 I owned. The 300SE got 16/19 mpg, the S420 got 15/20 mpg! Don't drive a 560SEL too often and the 300SE/L won't feel too slow. Second gear start kills the stop and go experience. Drag racer rear end ratio kills the freeway experience. Hard to believe the same engine in the W124 kicked 'vette butt in its day. My 300SE couldn't keep up with a V6 Camry. It's as fine a car as any W126 but my experience says the economy benefit isn't worth the performance and 'relaxedness' penalty.

Sixto
87 300D