Having been through a load of tall screens - Givi, Powerbronze, Madstad etc I got terrible buffeting no matter which height/size. The Givi Airflow and Madstad 22" were awful. In the end I got the standard BMW touring screen and adjustable screen mechanism from the 850GSA, and it's just about acceptable. It seems that smaller is definitely better. Of course, YMMV, but before you spend hundreds it may be worth checking some threads on here and 850GS.com.