I own a MKVIIM and a IX. I was surprised at the tire choice. No issue as long the load rating is met.
Tires for these are tricky. I have never done radials. I am of the belief that before changing to radials there are suspension rubber and other things that would need to be done to get the best ride and handling characteristics out of that type of tire.
The tires usually has a range 28-32 PSI, at least the one I’ve mounted.
You still can’t look at tires especially radials and tell if they are properly inflated. Radials still have a bulge.
Under no circumstance would it be advisable to exceed the manufacturers pressure!!!
I had MIchelin X’s on my Fintail Mercedes, not a fan. I’m sort of surprised as the MKIX is pushing 3 tons and I wasn’t aware those were able to carry that weight. Personally, I go check the tire and verify its load rating.
Regarding your excursion and high temperatures. I would bring extra hoses. They are now making a Kevlar substrate hose, I used to think those were overkill but with the limited numbers that the market services it no longer surprises me if they can’t make them competently and now have added Kevlar. There are a lot of problems with rubber parts, both in size and function. The vendors tend to opt for cosmetics than durability when calendaring the rubber for the process. All I know is my Father didn’t have issues like this when he drove them.
Racers use something called “water wetter” I believe its a surfactant that keeps bubbles from forming which negate heat transfer. A water and antifreeze mix is advisable and protects better than 100% of either.
I woukd recommend carrying extra hoses, a coil, cap rotor and a condensor, though condensors and rotors have been iffy as of late, hence the increase in electronic refits.
Have a safe journey!