I like the look of 20s too and am concerned about the ride. What I've decided to do is order with the 19s (unlike most, I hate 214 wheels and don't want the summer tires BMW ships on 20s), then switch out to some 20" 259s with Conti DWS or Toyo Proxes.

I'm hoping that the 20" + non-RFT will be a good combination. I do tend to take rough pavement and speed bumps pretty fast, so the 19s won't leave the stable until a good evaluation period is over.