In my experience, the key to keeping warm in the cold(Louisiana "cold" isn't really that cold) is to limit sweating and then change into fresh clothes before getting on stand.
I have a very high octane body. IF i'm moving, i'm sweating. I sweat so much my doctor prescribed me prescription deodorant for my pits and they sweat all day no matter how hot or cold. They define it as " Hyperhidrosis", and it's tough to manage when it's very cold. My pits and feet sweat ALL DAY!
With all that said, I want in on cold days (30* or less) in shorts, rubber boots and short sleeve t-shirt. This allows me to hoof it to my "staging area" where I try to allow myself 20 or so minutes to cool off before I made my final approach to stand. At this point I strip down to my undies and let me core temp drop to where i'm borderline shivering. When I get to that point I put fresh socks on, put on my bibs(leave everything fully unzipped) then put my t shirt back on and walk to stand. My feet are still going to sweat just from being in rubber boots so when I get on stand and everything is as unzipped as can be, I am still having to manage sweat. While my feet are still warm from walking I put on artic booties with hand warmers in them(they've been in every since I got to the staging area) and slowly zip up the bibs and add layers on top as needed. I have found it's much easier to add layers on my upper body than my lower body while in a saddle so i plan accordingly there.