I hear you - I’m in Oklahoma! I always say that guineas are heat tolerant, and I do think that they are, but they do show that they are hot quite often. Mine will hold their wings out and pant quite a bit, with a really fast rate of panting. If a chicken looked as hot as they do I’d be concerned, but my guineas so often look like that, so I think it’s just how they look when they are dealing with our heat. As long as they have shade and water I think that they are fine with most US temperatures.
My tiny keets have been in the coop in these hot temperatures and they’ve been fine too. The only time I’ve seen one with heat exhaustion was when a hen got tangled in the net covering my run in the heat of day and full sun. I don’t know for how long she’d been caught, but when I released her, her casque was very pale and she was panting so hard. I brought her a pan of ice water in some nearby shade and thought about bringing her inside, but she took off and headed to some shady areas. I figured that if I couldn’t catch her she’d be ok, and that chasing her would just get her hotter. She was still pale that evening and a little off the next day, but fine after that. So, when I wonder if our guineas are too hot, I compare them to how she was and usually decide that they are ok. I do put pans of cool water out when it’s really hot (over 100 F).