AC Schnitzer makes forged wheels up to 22 inches that will fit the X3(F25). They keep the offset at ET=30mm, and they keep the width down to 9 or 9.5 inches. Those wheels use 275/25R22 tires (Michelin Sport Pilot @ $456 each).
see:
http://www.ac-schnitzer.de/en/bmw-ca...heel-selector/
Here's the Schnitzer demo X3(F25) with 22's.