We raised FR's last early summer (end of May to mid July). It was the hottest summer on record.
We then raised CX end of summer-early fall (late Aug to early Nov). It was the coldest fall on record.
I was surprised overall - the FR's did very well in the heat despite having as many feathers as my layers (Black Java's). The CX did very well in the cold and wet, despite having so few feathers! The thing with processing the FR's in the heat however was the feathers stuck to sweat on our arms. (We skinned the birds, not plucked). And with so many feathers, I'm still finding feathers in the processing shed a year later! And in the run....and the tractors....and just about everywhere in the yard!
I did provide two extra waterers the last few weeks when it was so hot (over 95). And a few fans also to help keep 'em cooler. But they still foraged for bugs, chased and ate flying bugs, ate grass in the sunshine....just like nothing doing in the heat. Go figure! I'm hiding in the shade panting, and they're out being, well, chickens!