To pick one very tiny detail of your post and reply to it: For me, 50 degrees is the dividing line between winter parka vs. a lighter coat, and below 50 I definitely need a layer of long underwear. So hearing that you would wear a t-shirt down to 50 degrees makes it very clear that you and I have very different personal thermostats. I'd wear a t-shirt down to about 72 degrees, and long sleeves if the temperature goes below that.