Saw this older post but have some experience with riding a naked bird, a nacelle equipped bird and one with a full tall screen with lowers.
Naked bird is wonderful for around town-with a full face helmet it's a joy to ride under 45 mph. Above that your hanging on for dear life and getting beaten up. The nacelle smooths it out by keeping a lot of pressure off your chest but your head gets the full blast. I liked this for 45 to 105 but after about a half an hour the blast was getting my neck sore. I bought the SE with full size screen so I can pop it off when wanted. The bike comes with some pathetic tiny lower wind deflectors-I was noting a lot of buffetting at 75 -90 mph (closed track of course
) so I took the lowers and made ones about 6 times as large-big enough to the fender cleared. That made a huge change for the better. Even helps when the screen is off a lot. I think a wider screen with a gold wing vent would be even better and I have some emails in to Clearview in the USA for a retrofit for my SE. I have done a few 400 mile days and it's windy but tolerable.
If I travel more than 15 miles at speeds I need a screen.