CochinBrahmaLover, thanks for posting your question. Both it and the replies have helped me to put the issue of "how cold is too cold" into perspective. I've always thought that it is the amount of change in the temperature that is more important than the temperature itself. Humans are like that too, I suppose. Here in balmy Ohio, we had a day at 50F w/ rain followed by a dip to 20F, all within 12 hours. That, my flock did not enjoy. A couple of my birds wheezed for a day, and they seemed quite unhappy, but it passed. Basicaly, they got quite cold. Now, they're out and about like the change never happened (and they are not wheezing). It's still in the 20's.
I think it is mostly the ability of the flock to acclimate that is important, not simply the temperature to which they are exposed. Now I know that at some point heat is a good idea, though that point will likely never be reached where I am.