Arcteryx Proton AR? Atom AR?

Anyone here tried or fondled an Arcteryx Proton AR? I'm looking for an outer/mid layer for climbing between 15-20k'. I like the Atom LT but it doesn't seem warm enough for those altitudes, Nano Air even worse as the wind goes right through it. The Atom AR might be better but it doesn't look like it will breath. I really hate wearing a hard shell if I can help it. Ideas?

I've been curious about the Proton series as well.  Personally, I own an Atom AR and I would sweat to death if I actively climbed in it/used it as my mid/outer layer. However, I've never been to the 15-20k elevations, so I guess my assessment of the Atom AR might be a little off. The Proton AR and OR Uberlayer are about the same insulation weights that are comparable.

My limited perspective from swapping between an Atom AR / Proton AR / Cerium LT at an Arc'teryx store the other day - with the caveat that I obviously didn't get to go jogging in either, so I can't give any sort of rigorous comment on breathability, which I know is your central question.

Proton AR definitely felt a little less "warm" than the Atom AR or Cerium LT, but it's hard to compare synthetic to down since down usually feels warmer right away. I can't honestly say whether the Atom AR felt "warmer" than the Proton AR moreso than just "stuffier", if that makes sense. Proton AR felt the most rugged and breathable, while Cerium definitely felt the least rugged. Atom AR felt a little more roomy for layering. 

Personally I already own a Nano Air and Squamish Hoody - I didn't feel that either the Atom AR or Proton AR were different enough to push me away from this combo, however I'm not going above 14k anytime soon. The Proton AR could definitely be the step up in warmth that you're looking for while still retaining a decent amount of breathability.