It will look insane for sure! I had 20" 312 on my F10 530d (not ferric ones) but this time I will put on 20" Hartge Classic II on my upcoming AW F11 535dAM
+ some small changes on the car itself..
Will use the 18" M-sports on Conti winter tyres.. Will look totally wierd with 18" when I'm "used" to 20" but then again, I will not drive that much on the winter..