It only seems in the US that you get the same size on all four wheels. I wanted staggered setup to put more rubber on the road. In the summer at least. As I stated above I had a 2010 750ixL Exclusive, with also ran a 20" Factory staggered setup with DINAN Stage 1 without issue.
So far I put 500 miles on the F10 with Stage2 and pushing hard as I can in a straight line I have zero issues. In the corners it is wonderful. If you look in the F10 manual you will see it is a standard setup for the 20" wheel.
2013 550i X-DRIVE, M-sport, Imperial Blue, Black Nappa, DHP, B&O Sound, DINAN stage 2, M5 Grille, Escort 9500ci, Coded.