It is my assumption that the shock would "stiffen up" in the winter due to the oil in the shock becoming thicker as the temp dropped. Correct? Then I would assume both would do it. Bilstein HD shocks are monotube gas shocks.

Next question, if he's selling you on a gas Koni, it would be Koni Sport yellow I believe (twin tube low pressure gas). The Koni Special red (twin tube hydraulic) isn't a gas shock. Therefore the Koni Sport yellow would be a performance oriented shock much like the Bilstein HD, so I'm not sure I agree with this recommendation on the surface.

If you're looking for comfort as the number one criteria, I wouldn't suggest any Bilstein or Koni option at all. I'd be looking at a much less expensive Sachs/Boge option similar to OEM, but I can't make a specific recommendation as I personally value performance well ahead of comfort on my own car.

However, I do like a firm strut/shock setup on a car with soft springs because I have better control in transitions or high speed maneuvers. My daily driver is a 240 with stock springs but stiff struts/shocks and 14" all seasons. It rides well and absorbs bumps without being floaty. I'd call it soft, but precise.
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