Regarding air vents: nothing to do with the temperature, just the volume & velocity of the air that comes out of them. On a long night sector, it goes down the back of your neck, up your sleeves, dries your eyes out, etc. On one of our aircaft that is set to force 11-12, I had to fold up a bit of newspaper into a makeshift hat to avoid going numb around the ears!
It's a personal viewpoint, of course, much in the same way that some people can stand on a glacier at midday without sunglasses and others wouldn't even be able to open their eyes. I fall into the latter category, if you haven't guessed already...