It makes one hell of a difference, with the +6 wind screen it was like riding around in an oven. The wind screen's that I ride with are cut down to the top of the center brace for a couple of reasons. #1 air flow #2 if you have ever had your wind screen to fog up at 85 mph on the interstate you had better be able to see over or around that wind screen.
I can relate switching to the OEM double bubble windshields made a huge difference in the cabin temperature - before with the stock blade windshield which was pretty low my legs and feet would get pretty warm, but with the bubbles the wind swirls enough that my feet are much cooler. I am also finding that my new hood vent seems to have helped as well