Thank you Limaed and Widu13. I'm getting an idea on how these garments work as a system. I personnaly am keen to do more trekking than I do to find a spot to stop, so for these colder months I'm thinking merino base with a windshirt whilst active, then something like a down body or jacket when I stop. Fleece and waterproof if needed.
That's pretty much my combination, though I use a synthetic duvet rather than down as it copes better with the wet, although the pile/pertex is a good alternative. My fleece is fairly thin (Polartec 200) as it can be worn under my shell gear on very cold/wet days without getting too hot.