>>860338My setup:
>The North Face Summit Series VE25 tent>The North Face Summit Series Inferno -20C sleeping bag>Exped Downmat 9I am so cozy at sub zero temps that I sleep naked. Come at me old man winter. Though, tent placement is key to a safe nights sleep or suffering till morning.
Your entire setup is better suited for early spring through fall. The sleeping bag, rated at 0F isn't too exciting. The mat with an r value of 4 is pretty standard, but sub par for winter. You REALLY want a nice thermal gradient between your body and the snow underneath you. The 3 season tent will dump more heat over a 4 season tent.
Basically at this point in true winter conditions, you're either loading up on calories to stay warm or wearing tons of layers IN your tent just to maintain a comfortable body temp (or both). The tent is your lifeline. The differences between a 3 season to a 4 season tent are substantial enough to have a proper 4 season if you're going to bivouac this winter.