I actually am still wearing half finger summer gloves down to about 45. About then I switch to my lightest full finger glove, which is a Wells Lamont motorcycle glove, the lightest they make. It's hi-viz and reflective:

http://smile.amazon.com/dp/B005XQKE1G

I go to some level of insulation below about 25. At about 10 I'll switch to my full winter gloves which are semi-lobster-claw. I've been down to -25*F with those. Kind of thinking about getting some bar mitts for -5*F and below, where even with the warmest gloves my fingers get a little chilly.