Thanks for the replies everyone.
John and Matt, I'm surprised at your recommendations for heavier layers (260 merino, Cap4) considering part of my itinerary will be so hot (>100F a real possibility), are these shirts OK for that kind of heat? I was thinking 150 merino or lighter or a Cap1 type material would be better.
Stephen and Reggie, wasn't familiar with the Ampere or Manitou, will look at those.
David, a lightweight Smartwool was definitely on my initial list, along with Icebreaker, Rab, Stoic, and similar. Also preliminarily looking at some of the synthetics like Cap1.