you got that right Paul, the inline 6 sure is smooth. We recently took my wifes C230 on vacation to Florida (at the time I was still pulling my hair out with mine which turned out to be the bad throttle actuator), it was ok, it got great gas mileage, was smooth enough on the highway, BUT, my E320 fits around me like a glove and I missed it. Sliding behind the wheel of my car is like putting on a nice pair of worn in shoes. It just fits perfect and eats up miles effortlessly.
One thing that did bother me when we went to Florida was that I was not able to find a good comfortable sitting position to where my back didn't hurt. I bet I screwed with the switches for a half hour trying to get comfortable but was never able to. I don't drive it too often so I'm not really a pro at finding just the right seating position in it. She likes it and that's all that counts!!