Had these out in 40 degrees and sunny yesterday, never overheated, didn't get sweaty either. I run hot and sweat easily, so I was very happy about the breathability. The side vents are useful, but they're small enough that they're more of a bonus to breathability, I'd say most of the breathability comes from the fabric. On that note, the side vents are backed by mesh, but they are too narrow to be used as extra pockets.
The fabric is marketed as being stretchy, so I expected some level of stretch, but was surprised to find that it is very, very stretchy (in a good way). Zero movement hindrance at all. I struggle to find pants that fit well, and the cut combined with the stretchiness allows these to be fairly form-fitting while still presenting zero constriction anywhere.
Got up on some windy ridges and the wind resistance seemed solid as well - I didn't notice the wind, so no complaints. I can absolutely see myself taking them to much lower temperatures as well - there is just enough room to comfortable layer some thermals underneath. Even in cold temps I struggle with overheating/breathability, so I'm pretty excited about these. ( I haven't really gotten a chance to test water resistance, so can't speak to that.
The only potential downside I can think of is that the cuffs are a bit small. I was using them with pretty slim boots (F1 LT), and that seemed to be about the limit of the cuff, even unzipped. If you're running beefier boots maybe look at the mercury dynastretch pants, which appear to use the same fabric with a roomier cut. Overall these are excellent spring touring/scrambling pants (and I suspect will also make for some solid winter touring pants for people like myself who overheat/sweat easily).
