+1 for the 19s. I currently have a 40d M Sport on order, and deliberated with the same question. I think the 333Ms look great and the 19in 223M pretty average. I had a test drive with the 20s, on good roads and thought they were fine. Then I took a second test drive (in central London), again with the 20s and encountered a pot hole and also a speed bump, and was shocked at how rough the ride was over these. I ended up deselecting the sports suspension and going for the 19s as a result.

I'd had quite a few owners on forums telling me the ride was fine on the 20s with sports suspension, and I'm sure for them it is. It is subjective after all. However for me, and as the car is the primary family transport rather than my toy, I felt the set up I went for was better for us, and will still be a sport orientated ride. It's worth noting that are still some independent reviews complaining even this is too firm.

As ard suggests, in the unlikely event you were to take the car round a race track, the 19s would I am told be faster. The unforgiving nature and reduced flexibility given the reduced side wall costs connection with the tarmac and loses time. That's why race cars will always have a bit more sidewall. Tbh that was never a consideration for me though.

I agree, however, that the 20s do look better. So at the end of the day it comes down to what your priorities are, and how sensitive you are to ride quality. The ideal would be to test drive the 20s set up and look out some rough road.

Can't comment on the adaptive drive as it's not an option on the diesels over here...