Regarding the cut down windscreens, my mate Pat and I swapped bikes on the freeway one day and he said afterwards that he felt his helmet being buffeted a bit at 100kph. I realised this was happening to me also, but needed someone else to bring it to my attention. This is with the standard screen on my 2006 Venture.
I thought about this for some time and came to the conclusion that the angle of the screen is to upright (steep). This produces a near verticle obstacle for the wind to pass over, so when the wind hits the screen it's forced straight up and get's clobbered by the wind at the top of the screen, which blows the whole lot over and down onto your helmet, causing a buffeting effect.
I took the screen off and examined the mounting lugs in the fairing and decided with some fettling I could mount the screen in front of the lugs instead of behind, thereby changing the angle of the screen so that it had the same angle as the chrome trim at the base of the screen.
The effect of this is that the wind is redirected over the screen more gently and thrown over our heads (rider and pillion) instead on top of them. No more buffeting. It even looks better.
To achieve this you need to reshape the bottom of the screen, cut some off the bottom corners towards the centre and drill new mounting holes because when you change the angle of a curved surface, the curved alignment of the mounting holes changes. It's a bit fiddly but if you are carefull and mark it out properly it can be fairly straight forward. I used a small angle grinder to cut down the material and you need to just take off the leading cutting edges off the drill bit you use so that the drill scrapes it's way through the plastic instead of biting in and breaking it. By changing the angle of the screen you also lower the top edge while moving it back, about three inchs down and about four inchs back.
I also cut six pieces of firm rubber hose, about 1 cm long to fit behind the mounting lugs, where the screen used to be, so that when you tighten up the screws you won't break off the lugs. the bits of hose support the lugs so the screws go through the hose. The screen rests on the top edge of the fairing exactly as before and there is enough room under the trim to accommodate the button-head longer screws you will need.
I can now look through the screen if I slouch or over the screen if I sit up straight. I don't know why Mr Yamaha didn't do the mod' years ago.
Ron Henzen