I think I would have to agree with you on this thought about the stress on the Cornish birds, I have had the same here with mine but they always seem to pull through it ok, But tomorrow night it is supposed to be in the low to mid 20s here, my bantams will be comming in for the night.
Jesus is a very good breeder of bantam & large fowl Cornish, I have both from him & he is very helpfull, Thanks Jesus for great brood stock !!! They are doing great.
Wish I could help you out here but I'm just learning about this breed myself, got a new pic. of one of my chicks at about a week old now, what do y'all think ?