There was a good article not too long ago in Car&Driver or Road&Track regarding awd cars vs 2wd. The V6 in the W210 wagons is very torquey, especially off the line. I suppose that extra punch off the line could be a liability on ice. The transmission does have a "winter" mode that activates at the flip of a switch. Winter mode starts the tranny out in 2nd gear which makes takeoff on ice/snow much smoother. The new 4-matic system is an adaptation of the awd used in the ML's. It is supposedly a great advancement over the previous system but I have not driven enough 4-matics to say for certain. Any time you add the extra hardware necessary for awd you add some weight. Whether it impairs performance to the level that you find unacceptable is personal taste. MBNA claims the same 7.8 0-60 time for a E320 wagon with/without 4-matic. You lose a mpg on highway mileage but are rated the same in city driving. Draw your own conclusions... Since it does not have the ML's low speed transfer case you are surely saving some pounds there. Your best ally in winter is 4 good winter tires. I assume you and your friends already have a set of dedicated winter tires... An awd car with 4 winter tires and the usual MB electronic aids should be able as stable as one could hope for.
Hope this helps...Lee