I live in the Mojave Desert in California and it typically gets 105+ with 0% humidity here in the summer. That does not seem to bother them as long as they have shade and water. I have raised several sets of them to 6 months of age - I like them huge. I usually keep them in groups of 12 and they have free roam around a large pen with access to dirt and sun.
The thing to remember is that because of how fast they grow, you need to restrict the food input. They will literally eat themselves to death. If they get too much food, they will have leg problems and thus problems walking and they will also have heart problems and die suddenly - all from over-eating.
I have always bought mine from McMurray and they always provide excellent stock. My rule of thumb for 8 week old chicks is this - one full size canning jar full of feed for a dozen birds one in the morning and once at night. Go down from there with serving size on younger birds.
I also keep them separate from my other birds because my laying hens need to feed more and freely but the X-rocks will devour any feed they find so it becomes a competition between breeds.
Hope this helps.