My MB actually gets quieter at above 80 mph, the motor seems to have a sweet spot at about 3000 to 3500 rpm. I drove to Minneapolis and back last night 6 hours total, and after watching the autobahn show the other night, decided that I would make I-35 an autobahn of my own. 80mph+ all the way. Some left lane hogs though, but the light flashing technique usually works, I think because you never see that kind of thing out here, and the surprise factor gets the lard a**es out of the way.
Beautiful trip actually, and no speeding ticket. Didn't get very good mileage though...

DS
87 300D