I don't live there, but I have a 5-seater X and we drove through the south last summer. We had a lot of horrible hot weather and the AC was just fine. We are definitely not hot weather people, but we were very comfortable in the car and it didn't seem to be working overtime.
I will note, though, that was just my wife and I so we were only in the front seats. Maybe it was hotter in the rear, but I can't imagine it being terribly different especially with that big windshield up front. We did put on the mesh cover for the upper portion of the windshield. And we do have heat shield window covers for when we are parked in the sun.
But if you are concerned, a 7 seater will get you almost the same cargo space with even stronger cooling and more seating options.