What I have found out is that at 14" and straight up, my windshield not only looks good, but is very functional. The total height of my seat riser (without foam) is just a hair over 6". I have holes cut in the seat bottom and webbing, so it probably drops me an inch or so making the height about 5" which is still higher than the recommended 4'. I am 6'3" tall and when I drive the wind goes over my head. I found this out in my first attempt at wearing a baseball cap to protect my head from the sun. Even at highway speeds, the wind didn't blow my cap off. I drove my T for about a week before attempting to wear a hat because I just knew it would blow off. What happened was, I gave my sister in law a ride and she refused to remove her cap. So, in an attempt to teach a lesson and get a laugh, I sped up. I looked over and her hat was in place. That is when the light bulb in my head went off and I wear a cap with no worries.
Another thing to consider is that as air moves over the top of a convertible, it rolls over the rear of the car and buffets forward. Next time you see a person with long hair driving a convertible, note that thier hair moves forward towards the front of the car.
So, the 14" windshield, mounted straight up, is perfect. Even if you are tall and your seat is set higher than most. In my opinion, if I had gone with the slanted back windshield, that 1 - 2" you lose due to the slant, would have been just enough to cause me minor trouble, but trouble none the less. I'll never know unless I go slanted and I have no plans to.
My main concern was whether or not the glass would bow and possibly pop out of the frame while driving fast. I have noted no bowing at all.
14" on a straight up windshield seems to be the way to go. You get the "chopper" look and it still functions as a windscreen. Slanted back, you will get wind, but I dont think it would be unbearable. With a 10" windshield, I have a feeling you may as well not have a windshield at all.