Well, I got a WM bag about six years ago, like I said.

Is it worth it? Not from a purely practical point of view.

I'm not at all sorry I bought the WM bag. It is very beautiful. But I try not not to have any illusions about its rather minimal advantages.

I think I paid about $240 for the thing, rated to 40F (they've since decided that was too conservative and knocked it down to 35F). It weighs (supposedly) 17 ounces in "long" version.

Campmoor sells a similar bag for about $100 that weighs 2 pounds, rated at 20F, but probably good to 35F using rational standards (purely a wild guess.)

One pound is what a pint of water weighs.

The Campmoor shell is certainly more durable than the WM ultralight line.

I have an old duck down & feathers bag that is 35 years old, and is still (barely) holding up. (It stuffs down really small).

Down lasts and lasts, no matter the quality, if it's cared for.

(In fact I wonder, if you could graph the deterioration rate of 800 cubic-inch fill, vs 600, vs 900, what it would look like? I'm not even speculating, but it seems possible that the super-high-quality down could loose its "fill ability" at a faster rate than lesser quality stuff, at least early in its life.)