ST's are good coilovers to go with and they are essential KW Variant 1's. the ride quality should be good unless you are running 20's with 25 sidewall profile.

 

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I have Bilstein PSS9's on my e36 M3, and they are good, but definitely they can be harsh. I think its the lack of rubber in the strut mount. Great for tightness, but it transmits road noise. For my 545i, I chose to go with Koni FSD's and Eibach springs, and they ride just like factory, but just a bit tighter. But there is no substitute for coilovers, especially at high speed! The problem is good coilovers with minimal drawbacks are expensive, but prices seem to be coming down as more product is becoming available. I almost bought BC's with Swift springs as they have had very good reviews, but they were on a long back order, so I moved on. Anyway, if you want to maintain the cushy stock ride with some improvement, or if you have really big wheels, go with upgraded struts and springs. If you want razor handling, and can live with a some harshness, go coilover. Just do your research first.