It doesn't matter how hot it gets, I'm always in my jacket, full face, gloves, jeans (actually want to get real pants) and boots... ALWAYS.
Maybe it's the fact I have had to deal with REAL heat with way too much kit on that I know it's a mental thing and don't let it bother me. As soon as I'm moving it's ok.
Sure, Sunday was a hot day, but I spent the day in MX boots, heavy MX pants, my jersey, gloves, chest protector, helmet, goggles... I just drank more water. Looking at my arms today and all the bruises, I'm glad I wore all my gear.
It's hot, suck it up, wear some gear and save your skin! I've dealt with the tough guys that ate it without gear and I don't want to be one of them.