I do all of my load work up in hot weather, it may be uncomfortable shooting in such weather, but it's the only way to see max loads in the temps I hunt in. I don't always hunt in these temps, but the velocity difference, if any, between hot weather and cool weather is neglible in 90% of hunting.
For true long range work, I run the same loads in hot and cold weather, but I check what velocity I'm getting in the field and adjust my dope if necessary.
Yes, I would say that all IMR powders are temp sensitive, some more than others.
Hogdgon Extreme powders are what you need for temp stable powders.