It's been my experience that rubber bootshold the cold, so I won't wear them when it's real cold.I wear the Northern Outfitter's Expedition Boot. They claim they'll keep your feet warm to -60F. I've never hunted when it wasTHAT cold, so I wouldn't know how true that is. I've never been cold wearing them though.
This is a bulky boot, so I would only use them for stand hunting. Not real good for hiking/climbing.They are NOT water proof, but this shouldn't be an issue when it's very cold. Your feet will not sweat (worst enemy in the cold) in these boots either. I love these boots, and for $200, I think they're reasonable. Here's what they look like.