My 2 cents for high-altitude areas in summer where it "can get down to freezing." My experience is that the coldest temps happen early in the morning, just before sunrise, when I'm *smart* enough to still be in my sleeping bag. :) Evening temps, I've found, are maybe 5-10 degrees warmer.
I'm comfortable sitting around in my Nano Puff to maybe 45*. At 40*, I want to be moving around or have a solid layer underneath. Some of this depends on what I've got on my legs and it really helps if my feet are warm and I have a hat. I have a Montbell UL Down Inner and it's comparable to the Nano Puff for warmth. I think experiences will also vary slightly depending on how the jacket fits.
So, for that high-altitude summer trip, I take either my NanoPuff or Montbell Inner plus a WPB shell and I'm good. I will also have a midweight long-sleeve baselayer for sleeping that I can wear underneath in the evening. If it gets unexpectedly cold, I just slip into my sleeping bag. Not a big deal.