Treated down is not superior. The BEST sleeping bag makers in the world do not use any treatments on their down, and the three gold standard makers are 1) Western Mountaineering 2) Feathered Friends and 3) Valandre. The quality of down in these bags are all equivalent and about as good as it gets. The temperature ratings are conservative, the materials AND stitching/construction are top notch.
Best is to find one that fits your body type. I could swear by any of these makers as I’ve personally used them. Valandre has the most durable fabric (Asahi-Kasei 66 nylon) as well as the most meticulous stitch-work on their highest end bags but has very slim legs as the bags are geared for mountaineers. The shell is not as naturally water resistant as WM Microfiber and depends on DWR. The mummy cavity is 3D contoured. Anyone who sees the contoured construction should be impressed by the innovative design. They weigh a little more but the outer shell on a Valandre is so much more durable and doesn’t accumulate small punctures. The Shocking Blue is fantastic at 0 and below and is large to allow you to wear a down jacket within the bag to push the temperature rating. But slim legs. Western Mountaineering’s polyester MF (microfiber) is prone to snags but is ultra soft and breathable and again, naturally very water resistant although any water will eventually seep through if there is enough condensation pooling and dripping. Both of my MF bags have tiny holes sealed with Silicone sealer. I like WM because there is a width/size for all body types and it is easily available in the USA. The Gore Windstopper fabric is great and much more resistant to snag or puncture but obviously less breathable.
I own two Antelope MF’s, a Megalite (to be sold), a Valandre Bloody Mary, and a Valandre Shocking Blue as well as two Valandre Grasshoppers for family summer camping. I sold off two Puma GWS’s as I don’t venture into Uber cold. They’re all fantastic. I was a mountain climber in another life.
You can get warm down bags from many manufacturers, but I can say they are all inferior in construction or material quality to the three brands that I listed which you can think of as the Swarovski, Zeiss, and Leica of mummy sleeping bags.