WM bag questions

I need a warmer and wider bag than my 30 degree Marmot Hydrogen. The dimensions of the light, slim cut mummy bags at Western Mountaineering (WM) are smaller than my current bag, so I'm considering a 20 degree Alpinlite or a 25 degree Sycamore for the longer zippers and wider cut.

What makes the WM bags so much warmer than the competition? Is it the slim cut? The down is about the same quality as others, so does WM use more of it? Is the fabric more windproof? I assume the design is not a secret. Is it the US pride in craftsmanship?

The Sycamore with 2 oz. of free overfill is still $50 less than the Alpinlite. The bags are different widths, but that does equalize the fill weight. Is anyone using a wide cut WM bag and regrets needing to heat up the extra space on the inside?
Thank you for sharing your experiences and knowledge.
Joe

I have had my Alpinelite down to 10*. Once the bag warmed up I was okay thru the night. I was in an OR advanced bivy. I am not sure that the bags are any warmer. I cannot be in a tight bag - they freak me out sometimes - I have never felt that way in the Alpinelite.

I've had a Marmot Hydrogen, Helium & Lithium.
I've had a WM HighLite, Badger, Kodiak SMF & Bighorn SMF.
I currently have a WM MityLite, Sycamore MF, Sequoia SDL & KodiakSMF.
At 6'2" & 200lbs I'm mostly legs so I like the hip/foot girth of the WM semi-rectangulars (named after trees). The Sycamore doesn't have a collar but whichever jacket I carry makes a nice collar and will keep me comfortable to about 15dF if I need it to.
Some folks are good with narrow bags but I like to have room to move. Plus as I get warmer I can shed clothes and they stay warm in the bag with me. With the big bags I can also get shoes and water bottles inside to keep them from freezing. Though the big bags weigh more and use more pack space it's a trade off that's worth it for me.
When you buy a WM bag you're paying for craftsmanship and the best materials available. If you're Hydrogen is a long model the girths are 64"/60"/40". Look at the WM spec chart compare to see where you want it bigger for the temp range you need.

I just happen to have a Hydrogen and an Alpinlite with overfill. The Alpinlite is heavier but it is warmer and more comfortable. I'm not a big guy but I do tend to thrash about a lot in my sleep. So I don't want my mummy bag to make me feel like.....a mummy.

I never feel like I'm struggling to heat up excess volume in the Alpinlite. On the contrary, that bag gives me more room to wear extra clothing without compressing the loft and allows me to fine tune my insulation.

I'm not convinced that a WM bag is any warmer than any other bag of similar cut and loft. But they tend to be lighter. Of course that edge comes at a price. I think WM has a good grasp of what the their target customers want.

Wow! You should set up a store. I have never in my life had the luxury of owning more than two bags. It must be great to have a bag for every temperature range. I just lug my big WM Super Antelope with me in all temperatures, needed or not.

It helps to not have a mortgage and to be able to work some overtime to buy toys or those much needed bp items.