Born and raised here and have been climbing and camping in the Cascades for longer than I would like to admit (ok...a slight diversion in the Rockies along the way).
I've climbed in a lot of places and the Cascades is the HARDEST place to dress right. Anything seems to work in Colorado, for example. It's hard to get wet rolling around in their dry snow and 0 degrees there feels a lot warmer for some maddening reason.
In the Cascades, getting wet is real. Getting cold because of moisture is also real. I prefer synthetic clothing and down bags. Down bags are not hard to keep dry (enough) unless something really bad happens. I love the huge puffy cocoon surrounding me while I sleep and they last FOREVER. My main bag is 20+ years old and still going strong.
I might bring a down puffy while ski touring or car camping, but otherwise it's synthetic all the way.