Trust us. 20"s minimum on the F10.
When i went to 20" non RFT from my stock 19" RFT's i didn't even notice any change in comfort. If anything the ride might actually a little better. 21"s looks perfect but only if the roads are pristine by you. 20"s is the best compromise.
Mineral White/Mugello 2016 F85 X5M