Well south of the Dixie line from some people I know that have lived there or other hunters I have met online I got to say anything under 5C (Celsius dont know what that is in F sorry) is too cold for deer hunting
Now up here and for me personally There isnt a too cold to go out tempurature. I am too used to the cold and I love it as a matter of fact
Cold + Snow + Winds is much better then hot and humid
As for the deer if its old and windy from what I have been told they hide in the deeper parts of the woods to keep the wind away from them and they lay down
Dimitri