[steifan]

My 2006 euro 325i with m sport chassis is running stock springs and front struts still, but I replaced the rear dampers with Bilstein B8 Sport Plus (formerly Sprint) and I am still happy with that. Will be getting the struts for the front as well at some point but will keep the springs (no rust as it is only run in summer here in Sweden).

The Bilstein B8 is officially recommended in Euro Bilstein parts catalogs as replacement for M sport dampers. Dunno about the pricing in in your part of the world though.

If you want to replace springs as well it might be worth looking into Bilstein B12 kits (Bilstein B8 with Eibach Pro-kit springs) or perhaps little less costlier H&R Cup Kits (the comfort version perhaps) with twintube dampers instead.