I have the Bilstein Tourings on my Touring and they ride sort of like the factory BOGE but don't bottom out. You right the M5 rides pretty stiff already. Prior owner disabled the SLS and installed new rear springs with Bilstein HDs. When I first got the car I walked around it and pushed down at each corner. The back was atypically Bilstein stiff but the front wasn't. Went through his paperwork and he only had the back done and not the front. ??? I just ordered a front set of HDs from BavAuto so will do them the same time as the other front end parts. Former doctor owner loved his car but was mechanically challenged methinks.