I used a WM Alpinlite from Mexico to Tahoe, swapped out for a cheap Kelty synthetic 40 bag Tahoe to Ashland, OR, and used the Alpinlite from Ashland to the Canada border. There were some cold nights early, and unexpected rain in OR and expected rain in WA.
I was happy to have the 20 degree bag when I did. Just slept in thin long johns and dedicated sleeping socks.
It was nice having a synthetic 40 bag that I could get dusty, grimy, sunscreeny, mosquito-repellenty during the hot days north of Tahoe. The Alpinlite is too warm and too nice to do that to!