Not my car, but my dad had the HD Bilsteins put in his 87 300SDL. Didn't feel overly firm at all, certainly not enough that I'd have ever commented about it.

Granted, the last time I drove that car I was also driving my air cooled 911 and a Lexus SC with coil overs, so maybe my perspective was skewed. Even so, he seemed happy with them and he's a stickler for that stuff. I'll be replacing the shocks in my W126 and 123 with HDs when the time comes.