I sleep on an X therm year round, but I rarely see nighttime temps above 60f. Not a fan of hiking in the heat. I am also a side sleeper for the most part and I find it’s not so much the high R value that’s an issue, it’s the non breathable nature of sleeping pads in general than can makes them uncomfortable.
I sleep on a 14” thick foam mattress at home, so a high r value, but it’s breathable. On trail I sleep in silkweight long top and bottom which helps, but then again I don’t camp much in places with warm nights.
I did spend 12 nights in the Grand Canyon at the end of August, while rafting the river, and it was hot! I slept on the shelter floor sans a pad, sleeping on the sand, which wasn’t too bad. Many nights I used a wet towel as a “blanket,” and my wife, who is a cold sleeper did the same. Point is, I don’t find the R value of the pad to make as much of a difference as the pad/body interface.