I won't lie - lot's of summers here on a streetbike. When it's this fukkin' hot, I had a mesh jacket on, with all the padding - shoulders, back, elbows, kidneys. Just something to keep me from sticking to the pavement, if I went down and had to stay there, not moving. Full kit, though, besides the jacket material. Boots, gloves, fullface helmet. You had to have gloves, because the griips are too hot to grab without them. Just wasn't practical, or (healthy) safe to roll in a leather heatmit around your upper body, that won't breathe at all, and pass no air.
My $0.02 on riding in the oven.