I have done only a few flights above 13K' MSL in the east, never higher than that.
In other parts, 13K' MSL is a decent Soaring day.

So, I am NOT an expert!

Yes, metal rudder pedals can suck heat real fast.
Sunlight can help a lot.
Being damp (rigging, damp day, whatever.....) REALLY sucks heat.

I can only go by many years/miles hiking and likely lower flight altitudes for flying.
I will TOTALLY defer to others that think my "great altitude" is sorta the bottom of their "safe altitude".

Gotta think of where you are vs. where info is coming from.