Hard question to answer since everybody has different opinion on what is firm, soft or whatever.

I can say this. I installed the heavy duties on 92 300E and 90 300D 2.5 turbo earlier this year. I describe handling of both as firm, tight and not harsh at all. Going over speed humps on many of the streets around here does not unsettle the cars at all.

On the other hand a friend of mine who owns an independent Mercedes shop thinks the car is more comfortable with the comfort shocks; he says the comfort shocks make it ride the way it was meant to ride.