I use a +10 REI UL Nooksack https://www.rei.com/product/700564/rei- ... g-bag-long
It is about 10 years old.
Described as a synthetic down.
While it is described as 10 degrees it is much warmer than that so I have run cold on somed nights - Glacier NP comes to mind (Have not really tested in Sierras save 1 SEKI night) - to really layer up w long tops/bottoms and I believe fleece/socks too. Doubtful a hat or down jacket.
I never cowboy camp.
I am going to test it on solo in the Sierras over July 4 weekend. If I run cold, it may prove time to upgrade to a new bag like about 20-25 range.
After reading this thread and taking a peak at my Nooksack, plus related reviews and finding bag is heavier than originally thought, I decided to retire this from backpacking use and not test over July 4.
I splurged on WM Ultralite 20F. Used it 2 nights over July 4 weekend at Ediza and Thousand Island Lakes. Ediza ran a touch colder and I was fully zipped up w fleece top and shorts, while at Thousand Islands t-shirt and shorts all night with full zip only latter half of the night. Nights were likely mid-to-upper 40's.
Bag was super comfy, much better sleep, and rolled with me well when I tossed/turned - unlike my REI bag.
In short - I realize I run a lot colder than years prior. I am from East Coast, but 5+ years out here and my metabolism has shifted a ton. I am sure bag will be great when drops into 30's and a bit below, but I will definitely have to layer on quite a bit.