I just got back from a trip to the North Cascades and Olympics. I did not hammock above a few thousand feet, I'm glad to hear it can be done, sometimes! I did have multiple sweet nights along the Hoh river trail, however! The problem there was the opposite, an abundance of trees but mostly gigantic, to big to hang from. But even setting up camp in a brand new place in the dark, we still managed to find enough trees for the two hammockers, leaving our ground dwelling buddies on the gravel bar. And once we found those right size/distance trees, I was out like a light until the noise of my son getting the food down out of the trees, about 0730, woke me. I didn't even get up to take a leak, I was just out.
I used a supershelter to keep warm into the 40s.