The OE struts on my 2005 weren't Sachs, they were Delphi. The Bilstein B4s I used as replacements are pretty much exactly the same ride quality (meaning good).

I hear Bilstein B6s are firmer but harsher, which is why I opted for the B4s.

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Wayne
2005 BMW X5 3.0d (b 02/05)
2001 BMW F650GS Dakar (b 06/01)