I'm 6' tall with 29" pants inseam so I have a long waist and sit as tall as my brother who is 6'4" tall. Most windshields dump the air right at ear level (which is really noisy) or on my chest like the stock F800GS screen.
I really wanted to get out of the wind and noise and finally accepted the fact that I needed a TALL windshield, and style be dammed. California Scientific had the best information about how to determine how tall of windshield you should buy. They also have good information about the how and why of their design. I used both their chart and their measurement methods and determined that I need their X-large model.
I have about 30 miles with it so far, half of that in strong winds of 15-20 mph with gusts to 40 mph. No adverse behavior in the wind caused by the windshield. The airflow touches the top of my helmet. The turbulence between the quiet air and that beyond the bike is soft, unlike that on my 950 Adv. If I raise an inch out of the saddle I start to hear turbulence, at two inches it's getting noisy. Next test: can I put the peak back on my Arai XD3 - I bought it for the sun shade but it vibrated too much. Other good news: I can ride with the face shield open 1/4" or all the way. With the stock screen I had to keep it latched. I will have to get used to the top of the shield in the lower field of view; line of sight with the top is about 20 feet out.
CalSci has added braces to the windshield that are not shown on their website. It's readily visible in these photos. Installation was pretty easy.