Hi Brian- I currently own a '94 E500 (37.5k) and '94 E320 coupe (96k) MBs
I have driven a few S500 Coupes and the nature of these W140 coupes are distinctly different vs. the W124. They can be characterized as: 1) hightest luxo, 2) heavy, 3) not very nimble or quick, 4) a 1st class cruizer, 5) feels tons bigger vs. the W124. If this is your calling- - then the W140 coupe is for you.
(vs. your W124 V8- you may feel that the the W140 coupe- even with the 5.01 litre V8- is slower and more cumbersome)
Between the two- the W124 Coupe seems to hold the perfect balance given these characteristics: "size-wise" for a personal coupe, maintenance, luxo features and ride, gas mileage, and good looks....someone or other is always complimenting the E320 Coupe on its good looks
I've tried to rationalize a W140 Coupe for a long time and since the prices have dropped to be affordable- - it seems that now there's really an incentive to pick one up....except- - my intuition is telling me that the W140 will be a major challenge to keep in perfect condition...
...for now, I'll stick with my E320 Coupe. I just put over 1500 miles on it last week on a vacation to Baja Mexico and back to SF Bay Area- - no problemo whatsoever. I even ran a few gallons of Pemex 93 octane (Mexican petrol) with no apparent problems. The coupe was loaded with a completely full trunk, 2 mountain bikes w/ rack, and quite a few pieces of Mexican pottery on the way back. I averaged 22.5mpg over the 1500 miles and did the return trip from Mexico door to door in 8hours and 15 minutes (including 3 stops)
after a wash and wax to shake the vacation dust and grime- the E320 coupe is back to pristine