Craig,
I also have a 400E (non-ASR) and am planning to change the gear ratio to a 3:08 as I have a differential sitting on the floor in my shop. And the kicker is that it also has a limited slip in it.

Below is some verbage from another MB 400E owner and his remarks concerning the gear change:

"My engine turns 3,500rpm at 84 mph which is as fast as I can legally go in Colorado. I have no idea of what my fuel mileage is, as I pay no attention to it. My top speed is now 134mph. The gear change lowered my 0-60 times from 9.3 seconds to 7.1 seconds on a six run average at Denvers altitude of 5,200 feet.
I believe my car is now a sub six second 0-60 at sea level. The mid-range acceleration is fantastic."

That statement should make any 400E owner want to change his final drive gear.

Tobias MB
4 MBs