I feel that with today's DWR coatings and treated Down that the impact of the humidity is greatly limited. I would suggest shakedown hikes to hone in your hiking clothes. I have been below 20º using a Base Layer, Hiking Shirt, Cap 4 1/4 Zip, and either a Windshirt or Rain Jacket. I have not found the need to hike in a down jacket as of yet. Because the Jacket is for Camp and to hopefully aid taking my 20º Burrow down to colder night time temps (hoping to test it this January/February if I get the chance); I am worried most about the pack weight. A Synthetic is heavier and for the slight increase in cost... I chose the lighter down. So like Tundracamper is stating...you have to choose the system that works and makes sense for you. I want light.