Warmth and temperature ratings can be misleading because everyone has a different body mass and tolerance. Sitka gear is designed to be used as a system, and I think that the vest is a very important part. For me I sat in a tree stand all day this past weekend. Temps started out at 13 degrees and warmed to 25 throughout the day, but the winds picked up. I wore the base layer, mountain shirt, vest, Celsius jacket, with the 90% jacket overtop. On the bottom I wore the base layer pants, Celsius bibs, with a pair of 90% pants over that. I think what you wear on your head is very important. I wore the Celsius hat with my favorite wool stocking cap and a balaclava face masked pulled down over that. The Celsius hat stops the wind, but it also does not let me hear as well as I like. Overall I think it went well for me with wind chills in the single digits. It did not seem to bulky, but I will most likely need to add more under garment of light wool when temps get much colder like they do in late December when I seem to have most of my success from stand in recent years. I don’t know if this will work for everyone at these conditions, but this worked for me. Mike