Well I must admit I've never cycled in the 100's... that's some heat right there.
Heck I think my most sweatiest ride this year was actually only into the low 80's but it was so humid I was pouring sweat within the first 10 miles when it was still in the 70's!

Even though I talk about not caring for lycra you got me beat in the anti MAMIL (nice, never heard that one!), I got a couple to see what the fuss was about, so I do occasionally wear em (I'm a bit frugal, so use whatever I have till they fall apart). But I still prefer my cargo shorts. I even wear them running, won a 10k race earlier this year wearing soaked mostly cotton cargos, and also 2 weeks ago in an 18 miler I came in 11th/352, and I'm debating on wearing them in my October full marathon) and all barefoot. People just get too hung up on certain looks and being fashionable and whatever. Anyhow, I dig the 'gnome' look I say whatever works for ya.