On the one hand, I had a friend in singlet and shorts and baseball cap run a 17 minute PR. And while I was working a water stop at 30k all day, I saw 3 different shirtless guys go by. They made it that far at least.
On the other hand, I could never have survived with just that. I would have worn
a compression, T-shirt (probably short sleeve, maybe long sleeve…) underneath a singlet.arm warmers. shortswaterproof mittens over Castelli Neoprene mittensthin socks.skull cap