Are you using these on snowshoes? My understanding is that while technically possible, you wouldn't want to hike wearing only the 40 Below overboots without snowshoes/crampons/microspikes.
If just in your shoes, I'd recommend checking out the insulated VBL socks at RBH. Wear those and plastic bags to keep them dry on the outside and your feet will be toasty at 20 degrees. I didn't even wear liner socks with them, just the insulated VBL socks themselves.