Hi ! 19" rims make for a firmer ride especially with runflats, take the runflats off and it transforms the ride. The 19" give what I feel is tighter handling, as I have driven one with 18" rims and hate to say it ! but it felt like the rubber was flopping around corners, you know that feeling as you go left to right on a bend!!!! Some may say the lack of rubber with 19" is to harsh as I know many with 18" rims prefer the softer feel!!!! Opinions will be quite diverse on this subject!!!
Always said I would go back to a 6 series