I look over the top of the windshield. My line of vision is aprox 30' in front of the bike. It is tall enough that in heavy rain conditions I can tuck in behind the shield and look thru it. I use aviation products, Plexus, to clean and polish it so the water beads up and blows off when going down the road. By the way I have a kinda funny shaped body, short legs, long torso, 29" inseam. Hope this helps.
Windshields are kinda personal. Lots of factors to consider when chosing one. What is your normal seating position, do you slotch or sit upright? How far back do you sit, I like to sit a fair ways back which is why I use a badlander seat? Some folks like to look thru, some prefer looking over, I fall in the looking over my best riding pal like to look thru. So I think if 8" works for you than it is the "right" shield for you. As a side note I have used my windshield on my last three bikes, I really like it!
Just trying to get an idea. I've been using my stock windshield which is fine around town, but if I take a trip or do alot of miles on the highway ill need something bigger and was thinking 8" or 10" but would prefer the smaller shield for looks.
I used a 7" LRS Ultra on my EG. I'm 5' 10" and this height is right for me. I can see over with very little wind! I actually used a level to get a line at about eye height on the stock windshield then cut it off to experiment. worked great!
I have a 12" H-D windshield. I can see over it easily. I am 6' 3" and have the Police Solo Seat which sits higher than stock by a couple inches. The 12" shield is the factory height on Police Bikes.
I am 5' 9" also with a 30 inch inseam and use a 9" medium tint shield from Long Ride Shields http://www.longrideshields.com/
I can see over it just fine but can scoot down in the seat if I need to duck from the rain more. A little bit of wind around the very top of the helmet but not bad at all.
I'm 6"1 and have a long body with a 34 inseam so I went with the 10 inch wind splitter and it seems to be fine so far. I look over the windshield and that's the way I like it. Most of my riding is on highways at 75 plus so far this year the wind has been terrible so will have to find a day when it's calm to see if things change. May try some fork deflectors in the future just to see if it makes a difference in the wind.