Gear choice for crossing the desert in June

June 16-25 2017 I rode a 48 in 10. I left Flagstaff on the 23rd with extreme heat warnings forecast. The night before I put as many water bottles in my hotel room freezer as possible and the rest of a flat in the fridge. I read all I could find on riding in the heat , and was very glad I did. I keep a soft sided cooler on the pillion seat to keep drinks handy. I started early drinking a bottle of water every half hour as a minimum. As I got closer to Needles the temperature started to climb it was 116F at 10:30, shoulda left earlier maybe. It got up a bit over 120 by Las Vegas around lunch time, definitely should have left earlier. Before Needless I put a couple of frozen water bottles inside my lined jacket and soaked my Dri wear T-shirt. My Goldwing has a center windshield vent that when open blows on my chest. Keeping my shirt wet, controlling my airflow and zipper, and drinking a lot of water and Gatorade kept me surprisingly comfortable. I ate at Subway, Cold cut subs, if you ask nicely they will cut and wrap separately in 3, I ate a third every gas stop. I rode a bit over 1000 miles that day, and felt great. I never suffered any ill effects from the heat, good thing as I was a long ways from home still. I did email my forms and receipts in this September 13 but they are pretty busy so certificate is still pending.
Last Labor Day, I made one of my 'attempts' at the SS1000, from Kellogg, ID to home. I didn't plan well, though, and even though the early temps were in the 70's and only predicted to be in the 90's, I found myself riding through 100+F temps in the Eastern Washington and Oregon deserts. I was in jeans, flannel, t-shirt, light facemask, helmet. My normal summer riding gear has consisted of a long sleeve shirt of some kind, due to the SPF factor of about 3 billion, but I generally don't ride long distances during the day on those 100F days.

I thought I was getting enough water, but by the time I hit around the 450 mile mark, I was starting to feel very sick. I ended up pulling into Ontario, Oregon for a fuel stop and my thoughts were screaming at me 'get Gatorade NOW!' I grabbed a couple of 32 oz. Gatorades, and finished those with my half-a-Subway sub in about 10 min. I gassed up and thought about hitting the road again, but I almost dropped my rig at the pump and thought twice. I pulled over to a little grassy area with some shade and laid down on the ground for about an hour before I started feeling better. Fortunately, the sun was heading down and a little cooler temps were coming in. I let it get to the high 80's (after sundown) before I started off again. I called the ball on it about 140 miles down the road and stopped for the night. In talking with others, I've come to find just how close to a hospital visit I was.

I used to take high temps in stride, being a desert boy for so long, but I fully appreciate now, that need to keep the electrolyte level up, along with the fluid intake! Never again do I want to feel like that! I truly got lucky.
My opinions as others will chime in:
You need at absolute minimum to get a decent jacket. You need to be able to control ventilation. Wear one layer of picking material under it. You want air to come in at the cuffs and out at the neck. Now here's the magic trick. Dump a little water down your neck and presto, you get evaporative cooling. Works just like a swamp cooler.
Once you get this dialed in you good well into triple digits.

And stay hydrated as well of course