Congrats on the extra $$$, good feeling, eh?

Not sure about the other locations on your list, but for a JMT hike - 30F rated at minimum for a July/August trip, and more like a 15F - 5F for closer to shoulder seasons trip. We had freezing temps and snow during the first week of August going over Donahue Pass and down to Red's. High elevation weather changes on a whim - not our whim, unfortunately.

With proper precautions down is more than adequate for Sierra travels. I love my down quilts. Higher quality down gear is very light and compressible, and it'll last for years. Western Mountaineering and Montbell seem to get consistently good reviews for being accurately rated. I was very tempted by a Summerlite or a Super Stretch, but have been controlling myself to save money as the gear I have is fine.