I own the 200, 400 and 600 tops. 200,400 bottoms and a 600 vest. I often combine these without any shirt under my wool outerwear. I'll often keep the 600 sweater rolled up tight in a pack and if I really start to shiver or if very windy and heat robbing out, I'll take off coat and pull it on...its a full zip.
It breathes, so if you keep your outer coat off and walk in with just the ulfrotte layers on, it breathes pretty well, when you stop, put the outer coat back on.
Every body has different abilities to fight the cold, I chill down fast. I would get rid of a lot of stuff before I got rid of any Ulfrotte. I love the stuff. Socks too. Buy the 400, you won't be sorry. Never know when the cold is gonna get ya, be ready.