I've got adjustable GC Koni's for an e30m3 in the back of my car, well the front, too. Seems to ride fine to me, and while they might complain about my driving, they don't complain about it being harsh.
Don't know about the Bilsteins in particular, but e30 stuff doesn't seem too bad in general.
Oh, note; my suspension is all e30m3, so I don't know if they'll bolt into your car. YCarMV.