I've found that snowmobile boots (of old) slipped up & down on my foot too much when walking.

My REALLY cold weather boots are Sorrel felt pacs W/ a supporting insole/footbed inside the felt liner. (& I always use thin neoprene, seam sealed dive sox as a VBL with the feltpacs) These boots are good to -40 F/C.

For emergencies I carry a pair of Neos W/ feltpac liners & thick sox in the trunk of my SUV.