Had the opportunity to demo various sized Klock Werks "Flare" windshields on my '18 SGS.
I'm 5'9", short inseam; 30-31", long torso, and I wear a helmet. I like to be able to see "over" the windshield. I currently have the 7" Harley Windsplitter on my SGS. It works find below 50, but as I approach highway speeds and at highway speeds, the buffeting is very noticeable and after awhile gives me a headache. I'm not looking for a "quiet" pocket of air, I'm just looking for "smooth" airflow. I have a removable windshield on my FLSS, which necessitated the "fangs" to get rid of the buffeting. I have no issues riding my FLSS on the highway without any windshield for extended periods with the air hitting me on the chest and helmet, as long as the air is smooth. I've also had numerous ADV bike where I'd usually have to buy 3 different systems till I found one that works.
My local shop is part of the Klock Werks demo program. I tried the 6.5" and the 8.5".
The 6.5" - It's actually taller than the Harley WS Allows cooling air to reach me. Works well till about 60 mph when the buffeting starts to get bothersome, By 75 mph it's barely better than the Harley WS. Or at least, if there is a reduction of buffeting, it's not noticeably so. On the downside, the distortion where the compound curves is is very noticeable. BUT it's low enough you forget about it or don't notice it when riding. And you'll most likely never had to look through that section.
The 8.5" - With this shield I really had to sit up straight to comfortably see over the shield where I wanted to. IF I slouched, like I would during a long ride, the edge of the shield was right at eye-level. So already a big negative for me. The distortion "line" where the compound curve is much higher due to the taller windshield. Not quite in the way but if you look through the shield, its noticeable. Performance was pretty good, It allowed enough air through at low speeds. At highway speeds it was much improved. While some buffeting started around 60-65 mph, I was able to go 80mph before it became the same "annoying" buffeting. So it seemed the 8.5" was better for quiet air, but having the top edge of the shield in my line of sight was a huge negative.
In the end I didn't buy either. The 6.5 didn't do what I wanted at Highway speeds and the 8.5" had me looking right at the top edge. Now that I've demo'ed a few, IF I was to buy right now, it would be the Klock Werks 6.5 as it is slightly better than the Harley WS 7". With all this said I've got an 8" Freedom Shield on order. Hoping it's better...
So this just MY experience... YMMV....