Its more the size than brand for protection.

As big as you can get,I've always had big ones and you still need to adjust them to get the best coverage,My first windshield,Almost 40 years ago was a small one and all it did was put more air in your face. I'm only 5' 6 "

I'm 5'10" and have for the past few months had the Suzuki windshield I think it's great, the bike is more stable in the wind, including sidewinds, (a real consideration where I live).  It does put more air in my face but with a full face helmet and Willey X motorcycle glasses I don't really care.
RC

Mine is SlipStreamers Falcon SS 32-20, pictured at the very end of page 2 in the 2nd link of Versl's list above. I meant what I said about it !

For size, I bought the 20" (16 would be too short) model, and I can only tell you that I am 6.0 ft tall, and adjusted to the lowest position, I had to cut 1 1/4" off the top to allow me to see over the top. Actually I now have a choice to look over or thru it.

But the cutting was very easy using a fine tooth saber saw and fully masking tape the area. After sanding the edge, you can't see it was ever cut.

This shield is adjustable up/down on the fork by 2 1/2"

Yep, I had the spitfire also,...... mine was 5" above the headlite, and I still had to cut the rods off. But it was a nice sheild if you like small.

babyhog, I think the shape of the handlebars and where you place the grips on the bars make a difference. Just sayin' to watch out for interference when mounting. The tanks are thin, and sometimes when you leave the bike on the sidestand the front wheel will clunk to the left denting the tank in front. And yes, the Spitfire makes a big difference to me, too.  

Nothing noticable for mileage, but I'm never on any straight runs that give consistent mileage anyway. But I would guess w/ the arodynamics of it, I would think that at speed... mileage would increase before it decreased.
Yes, it is a drastic improvement over the much smaller spitfire, and a friend says it is a somewhat of an improvement over the OEM Suzie windshield that he traded out for it. But don't let me mislead,.....when its 40'ish out there, this ole guy is riding in something w/ a heater in it !