I've had the mountain hardware ghost whisperer for a while. It's 800 fill down with Qshield (their brand of waterproofing) and it works pretty well. It's not waterproof, but I would say it's water resistant.
If you're talking about a light drizzle or snow or a quick, accidental, submersion, I think having a shell with a tight weave is more important than the treated down.
I think I speak for everyone when I say that using a wet bag, quilt or jacket of ANY material is miserable.
Hope this helps. Cheers!
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"Without craftsmanship, inspiration is a mere reed shaken in the wind." - Johannes Brahms