I tested an old ebay acquired 21 & 1/2" tall Memphis Fats screen last night on my Speedmaster. I had the screen tipped back a bit past paralell to the forks. I'm 6 feet tall, and the top of the screen fell right into my line of sight, so it's off of the bike, and back to ebay next week. It did push the wind up and over pretty well, but I found that if I crouch down, I wasn't happy about looking through a windshield to see the road ahead. That's no fault of the Memphis screen, just my preferences.
I road tested the bike with no shield, but the updraft on my Shoei St Tropez half helmet wasn't something I want to live with, so I'll bolt up the Roadster screen again for now. The Shoei has a lot of surface area on the bottom edge, and may grab the wind a bit more than other types of helmets. I can't say for sure. I imagine the helmet visor is a large part of the updraft too.
I'm convinced that in my situation, my helmet is part of the windscreen buffetting issue. When I attach a snap on full face shield, it cuts the buffetting down to almost zero.
