Supplex is woven; Coolmax is knit That’s the big difference, plus Supplex is nylon and Coolmax is polyester. Supplex is usually not stretchy, though it can be made with some stretchy material added in.
The knit of Coolmax will feel softer.
But the nonclingy nature of Supplex might feel cooler in hot weather. OTOH, Coolmax is a bit more breathable, which could help it feel cooler if you sweat heavily.
Supplex resists rips and abrasion better.
Supplex dries faster.
Supplex is wind-resistant. Coolmax is not.
If you are talking about paddling or hiking wear, I’d choose a baggy Supplex shirt WITH VENTS over Coolmax, for the 90/90 day you mentioned. Even if you soak the shirt with sweat or water, it dries more quickly than Coolmax does. If you get the vented long-sleeve shirt with roll-up tabs, you have 2 shirts in one. During the heat spell in AK last summer, I wore Supplex-type woven vented shirts and pants. In addition to drying quickly, they kept my arms from getting sunburned (no need for sunblock except on face) and kept the bugs from biting through.
Great sun and wind shade; tough as nails. I have owned one supplex shirt for over a decade and stil paddle in it. Incredibly fast drying. Almost as cool as light cotton in the desert and with a UPF of 40 much better UV protection.
Coolmax probably also holds more body odor than supplex at least in the socks I have noticed that, and so have most others. In those temps I would wear my railriders adventure top made of supplex.
hmm ALL my socks are cool max, No smelly feet… Cool max is pretty breathable… I don’t think supplex would work as a sock it doesn’t breath very well, so your feet would get clammy in hot weather, just like the gortex socks…