I have the 8.5" on my street glide and I wish it was about 1/2 taller with the stock seat on the bike. The ultra seat has to be a good 1" to 1 1/2" taller than the SG so I think you would want the taller shield. I'm 6' and look about 1 1/2" above the top of the shield with the stock seat.
I put a 8.5" on my SG. I'm 6'4,and it made a world of difference to me. No more wind hitting me in the face and chest. And still short enough I can look over the top of it, and not through it. Biggest difference was how it "planted" the front end. It is glued to the road now.
have a 2015 SGS. put on the 6.5 klock werks windshield and it made a big difference over the stock one. My face was getting beat to death by the wind. I'm 6' and have the stock seat.