I've driven a 328i with m-sport and a couple of 435i GC non m-sport. I own a 435i GC M-Sport. The m-sport does seem to stiffen up the suspension but it's definitely not too harsh. This is a bmw after all not civic with cut springs. I think you will be fine. Also you can change from comfort mode to sport which I think makes a difference.
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435i GC
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