I think the tires are carrying close to their maximum. My suggestion is to load up, and have each axle weighed at with scale. You will then know for sure what load capacity tire you need, on the front and rear axle.
In my experience, a tire running in super hot climates is more subject to fail ahan colder climates. I have ran with bigger tires in the rear, but not on a 4x4 vehicle. I might also point out, a lower load capacity tire typically will have more sway than a tire with the stiffer sidewall.
Wayne