The key is that high gas pressure monotube shocks will almost always give a rough ride at low to moderate speeds. There's a reason why they are shipped OE on almost nothing.

Bilstein B6es are high gas monotubes.

I've owned a lot of monotubes. Bilstein, AST, Moton, Ohlins, Advance-Design... Might be forgetting one or two in there. The only sets that really rode well is the heavily customized set of Bilsteins rebuilt to my tastes by FatCat on my E36, and the Bilsteins on my truck. Every other set, including many sets of Bilsteins has had major ride quality tradeoffs.

Bilstein B4s are twin-tube shocks, like stock. They're a little stiffer, but they ride well.

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2011 M3
2006 Sierra 2500HD 4WD LBZ/Allison
2004 X5 3.0i 6MT
1995 M3 S50B32
1990 325is
1989 M3 S54B32

Hers:
1989 325iX
1996 911 Turbo