Under Armour
I swear by the cold gear tights and mock t's. Even double up on the mock t's when it is really cold. It is very flexible and I am able to draw my bow and pull the gun up quick when I need to. U/A allows me to decrease the bulk I have to wear under my hunting coat. Just purchase a U/A hunting coat and can't wait to try it out! It is nice finally figuring out a system to keep warm so I can stay in the stand longer.
By the way I hunt Long Island, NY up until the last possible day (Dec. 31st) and also hunt the Attica, NY area so I have definitely experienced the cold. Maybe not like Wisconsin though.