Yes, I have gone with 21's and I have AC Schnitzer coils. The coils lowered the car about an inch which covered the gap between the wheel arch and the wheels very well. The ride is still very forgiving and I have yet to run out of travel. The car is still very forgiving in mid-corner bumps and with the 21" wheels, there is the same ground clearance as I had with the stock wheels (pretty obvious with an inch drop and a wheel diameter increase of 2"s). I have to agree the M-sport option is very nice bit it was not an option at the time I purchased my car.
If you would like a great set of 21" wheels without the crazy prices of AC Schnitzer, contact Rob at Strasse Forged. He is a great person and would customize wheels anyway you like.
If you have any questions, please feel free to contact me.