The right windscreen depends on you.
Your height, your inseam, your riding posture, your tolerance level and your expectations. Since there's only 1 of you (I know, crazy assumption), the best thing to do is read, read, read and then guess at which one works for you.
I can tell you, if you are 5'10" with a 30" inseam, heavyset, like riding with poor posture (kind of hunched forward with your ass scooted back on the seat and your toes on the footpegs), you came from a cruiser with no windshield, and you wear an ARAI Quantum/f, then, like me, you can cut 3-1/2" inches off the top of the screen and be pretty comfortable. With that said, I do, currently, have a replacement GIVI shield on order.
Good luck with your choices.