I have a Cumulus Teneqa 850 bag with overfill. I also have a WM Alpinlite.
I had the Cumulus totally customised to my liking. And when I rolled onto a hot stove and melted parts of the bag, Cumulus repaired it and added even more down at my request, for very little money.
I’ve slept in it at around -22F or so and have been just toasty. I would say it’s simply the best bag I’ve ever had. I chose Pertex Quantum as the shell fabric and that is an awesome fabric, super water resistant. The down is excellent, I always feel like I’m crawling inside a fluffy cloud when I get in.
The Alpinlite is also an awesome bag. The zipper guide is better in the Alpinlite, but that’s a minor thing. In my opinion they are equal in all aspects of quality.
If I lost the Cumulus today, I’d order a new one tomorrow, that’s how I feel about them.