I am no PNW old salt, but back in the day I did my share of the cone peaks, a lot of High Sierra trekking, and some high altitude trips in Alaska and South America. What you'll need depends on the season, and what altitude you start from.
I don't recommend down if you expect to spend hours in rain, as everything gets sweaty, damp, while toiling upwards, even under the most bomber rain shell. Under that condition, you'll appreciate the fast drying characteristics of fleece.
I don't recommend down for a layer when performing heavy physical effort, even in pretty cold conditions, because it will absorb your sweat then freeze somewhere within your layers, especially in the down, which tends to be one of the outer layers. Over time the accumulated frost in this layer will either melt and defeat the insulating qualities, or accumulate and form clumps of ice entrapped down, which also defeats the layer's function.
I find down is best used for at-rest situations: while providing belay, rest breaks, and in camp. Given my attraction to high elevations and snow, it is ironic; I hate cold! The setup I resort to is considered overkill by some, but bad experiences with cold compel me to such practices.
I use the typical under layers - long johns and fleece while under way in the cold. I carry two medium weight fleece tops, one oversize to fit over the smaller one without compressing the insulating layers underneath. A single fleece suffices for the medium cold (high 20s), while the second fleece added will take me to the low teens. When at rest, I'll break out my down layer(s) and wear on top of the fleece. If there is a breeze my hard shell goes on top, regardless what other layers are utilized.
In really cold conditions I'll add a third fleece (2 sizes larger than my normal size) over my other fleece. And the down clothing I bring will be rated to address the temperatures I anticipate. Thus a puffy or two are used for conditions down to the 20s, while I bring more lofted down for lower temps.
There are two other consideration that need addressing: what goes on the bottom and what to wear in camp. I am a big fan of cycling tights for my legs. These can be combined with long johns, and when worn under hard shell pants they provide huge warmth for the volume/weight. At camp I'll continue to wear my active wear layers, allowing body heat to evaporate accumulated sweat. But eventually I change to my camp attire, which is my sleep wear long johns, and my aforementioned down layer(s). If it is real cold, I bring down bib pants for additional warmth while in camp.
You can see the answer to your question is not as straight forward as one would hope. In reality a mountaineer's layering strategy often overlaps with their chosen sleep system. I don't like feeling bound up, so prefer sleeping in just long johns, socks and a balaclava, and rely primarily on my bag for warmth. But many will cut a couple of pounds from their kit by relying on fleece or down clothing layers as part of their sleep system, thereby getting by with a lighter sleeping bag.
Lastly how you care for your layers while out on a trip affects their performance. Let your stuff get wet and fleece will be less effective, and down even more more so. Thus this topic leads to another topic entirely: how to maintain performance of your layers while on a trip. You'll need methods to protect items from moisture, and a set of techniques for drying out items that become sweaty damp. The best strategy is not allowing moisture to accumulate in your layers. Protect items from the elements when not in use, and regulate physical effort to minimize sweating into your layers while under way. I'll layer up just enough to leave me feeling cool, while under exertion, then limit my effort (going slower) so I don't sweat excessively.
There is much much more to this topic than I address here. We haven't touched on hand wear or head wear. But what you should take away for my post is whatever layering options you select, make sure outer layers are sized large enough to fit over under layers without compressing loft. Thus my hard shell drapes over me when I have no layers underneath, like dad's coat on his son - not stylish, but effective. Additionally you will need more layer options in your closet to address the PNW, than most other regions, because of the wide variety of weather conditions you'll encounter. I found more success equipping for Alaska high peaks than the PNW, because of the widely variable considerations one must consider whenever stalking one of the PNW cone peaks.

Above - A short rest stop, just short of Bishop Pass, Sierra Nevada. High altitude and late season has the morning temps hovering in the teens. I am wearing a long john top, cycling tights, a fleece top and a hard shell, fully un-zipped, while hauling my pack to the pass. Note how over-size the shell is, to accommodate layers I may add if I get too cold. I am a M size; this shell is XL. I am not warm, nor am I uncomfortably cold. This minimizes sweating into my layers.
Ed