I just swapped wheels from the M3 to the Z4. Rides fine, no rubbing at all with stock suspension.
Apex ARC-8 18x9.5 et35 Square
Hankook R-S3 265/35/18 Square
Apex 5mm Front Spacer
Apex 12mm Rear Spacer
Apex 75mm M12 Wheel Studs
I plan to stack a couple sets identical to this so I can run them on both vehicles at the track or autocross. If I can scrounge the $$$, I'll do the widest staggered EC-7 setup that I can fit as my street setup on the Z4.