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.
2015 750i X-DRIVE, M-Sport, (born 3/6/2015), Moonstone Metallic, Ivory White/Black w/Honey Walnut, ARS, B&O Sound, Escort 9500ci. VO and FDL Coded. BMS Stage 1.