Patagonia Cap 2 or Merino 2 for the JMT?

I would also consider Icebreaker and I/O Merino if I could actually find weights for these pieces. I can actually get better prices on these products.

KJ

A cap 2 top would be more than enough for August on the JMT, especially in a 20 degree bag (unless you run super cold). It would be a great top to take on the trip. And you won't need any extra sleeping pad R value — your temps will only be lower 40s, high 30s at the coldest. But its nice to take a CCF pad for just throwing down and napping on the spot without worry of puncture.

the Cap 2 is going to be essentially the same as your Phase- a lightweight, breathable syn top

I wouldn't invest too much weight in "sleeping wear", I don't think bottoms are necessary in August-if you're adverse to sleeping in the clothing you hiked in- take an extra shirt and a extra pair of boxers

Cap 2. Synthetics are generally going to be warmer for their weight than wool. The benefits of wool are being warmer when wet and not getting stinky easily. Neither of those things are going to be important for sleeping clothes.

My personal experience?

I found Capilene to be incredibly itchy to sleep in. meanwhile, I found wool to be a delight. I returned my capilene baselayer and have been sleeping and living in my Smartwool Merino Wool Baselayer for a year now. We're engaged, the wedding is in January.

I hiked it in August this year. I never hiked in the Icebreaker 150 leggings and Ibex Hoody that I brought, but I did typically wear them from the time I got done hiking for the day to the next morning when I started hiking again. I think they worked well. If I were to do it again though, I'd probably buy the 200 weight Icebreaker bottoms. My legs still felt a little cold sometimes without a campfire/above treeline.

I should add that they didn't stink at all by the end of the trip. My synthetic baselayer was rancid though.

Probably not considered UL, but i like to carry a set of light weight silk sleeping clothes, just for sleeping. If any of your day wear is itchy, you can wear the silk beneath it and be fine, and silk is surprisingly warm for it's weight.