I've traveled with no insulating layer on the last couple of summer trips, and found that I really don't need it. But it feels weird not to bring it.
I'm not particularly warm-blooded either, but I suppose male with an active person's metabolism. Still, I spent an enormous amount of time outside on the last trip, up high in the mountains, on rainy coasts, getting bashed by all kinds of weather. And I had no desire during any of that to pull out compressible down safety layer.
I think what I sacrifice in total certainty that I will never feel cold is worth not carrying a clothing item that I really almost never use. If the weather is cold I can wear fitted t-shirt, a little bigger t-shirt, sun sleeves, short sleeve button-up shirt, and a hooded Gore-Tex shell. Maybe a little wonky, but I do really dislike carrying stuff I don't use.
That's got to be just me though, right? I'm a little bit of a maniac about packing light, particularly since I carry all of my stuff under my own power from place to place quite often on a trip.
But anybody else cut any warm layers lately for summer travel?