Hmm! Interesting.I give no guarantees my first yr with them but I have been told by many they are winter hardy, even by someone that has them in cold Maine and hatched chicks in December, before I got them, and I was still definitely skeptical.
We've only had down around zero F and for not very long periods this winter and they have always been the first out of the coop like it's nothing. I seriously figured they would be huddled trying to cover up the bare parts and sucking their necks down like turtles. Nope, doesn't bother them a bit.
I even have a trio in a sorta tarp hoop coop with a completely open side, no frostbite, ventilation definitely good.
We do get winters -10- -20 F below and miserable windchill. Two and three yrs ago was months of around -5 to 0 F with 20-30 below windchill but I didn't have naked necks then, silkies leghorns and polish weathered it just fine.
I don't think I would want to live where -25F is normal :O
Would probably still have to bring 'em in for cold snaps, but as long as they can take down to -20F they'd be no more hassle than my bantams.