In my experience, the #1 factor in cold feet in a stand....is the stand. If you rest your feet on a bare metal stand, you are going to lose the battle no matter what boot or socks or warmers you wear. Use a foam cushion like a nemo switchback or a thermarest z seat under your feet. Something as a barrier between your feet and the metal stand.
Some other random thoughts...
Alphaburly 1200+ with room.
Wear a liner sock and a heavy wool sock, that leaves room.
Space = circulation
Use a merino insole like the superfeet merino grey or sidas 3feet merino.
Keep your core and legs super warm. If youre cold up top or your legs, your feet are going to pay the price.
Hand warmers need oxygen to get hot. Stuffing them in a waterproof boot, with a few pairs of socks, they arent going to get oxygen, so you are just stuffing beanbags in your boots that take up room.
Use the hot hands/feet on the outside of your boot by your toes - either the sticky version or with tape. I think I saw this on a Clay Hayes video on youtube a while back, and it actually works. The handwarmers get oxygen and produce heat and warm up the toes of your boots. And they arent inside your boot taking up valuable room.