I did a 45 mile ride on memorial day.
Headed out about 8:30am and it wasn't too bad but by noon the temps were in the mid 90s.

The last 10-12 miles were nearly devoid of shade and it damn near killed me.
I drank a 100oz camelbak and a 28oz bike bottle over the whole ride.
This equates to exactly a gallon of water.
I actually ran out of water about a mile before the end.
I will stick to 15-25 mile rides when its that hot.
I will save the 50+ mile rides for the fall.

However with that said I still commute about 10 miles each way when it is that hot.
I can do the short rides in 90+ heat, especially the morning part, but forget about the tours.