I'm pretty sure that the OE Bilsteins are different from the B4s. That said, I'm very happy with my Bilstein B4s. You definitely want to do the rears when you get a chance. Hopefully they come off backorder sometime soon.

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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