FastAire is having a 20% bike week sale now and I couldn't resist ordering an Aero 9". I like to use the taller ones with a recurve for longer rides. I have the 10" already, but it was just a hair too high for my likes. I think my windshield collection is pretty much complete now. Pretty happy with the FastAire shields and would recommend them.
Interesting, I'm currently using a KW 8.5 and have used the 6.5. The latter is sometimes a little too tall and the former a little short so perhaps a 7 inch might work!