Just thought I would share my thoughts as a smaller rider (just under five feet). I recently installed a Memphis Slims 15" windshield and am very happy with it. The 15" works great for me (tilted in). It is easy to see over and I do not get any helmet buffeting. They say it is better to look over it vs. through it -- if you get caught in the rain it is hard to see through a rain splattered windshield.
Of course, the right size depends on your height. I am posting this because it was something I really struggled with -- it was hard to figure out which size windshield would be right for me. In the end I followed some guidelines I found online which said when you are sitting on the bike, the top of the windshield should be between the tip and bridge of your nose. With that in mind, a taller rider would typically want a taller windshield (the Slim comes in 17" too).
It is a quick change one so it comes on and off in under a minute which I like since I like to ride without it too. It was very easy to install -- took less than 15 minutes for the initial mount. Since I have a purple bike, I got the one with the purple gradient: I like the way it looks with the purple -- it could be a girl thing.

The windshield is available in clear and a solar tint as well.
If anyone wants to see it, I will be happy to post a pic.
Yep, better to look over than through, for the very reason you state...and as you say, without the helmet buffeting too.
The Memphis Shades site is a good one with all the dimensions and guidelines. We've bought from them too.