Western Mountaineering Rectangular Shaped Bags

I am looking at the Western mountaineering Sequoia and Kodiak sleeping bags for ~0*F use. I currently have the WM alpinlight and Puma bags, but the temperature range of both bags is not quite ideal for 0°F use.
I have always owned mummy bags, but I struggle a bit in them (being a side sleeper) even with a 64 inch shoulder circumference. So, does anyone here have any experience with rectangular shaped bags for "cold"weather?

Appreciate the help.

I've seen a sample of a rectangular below 10 celsius (14F), it was massive.
You need a draft collar and proper fitting hood when you get in those temps, or else you'll be freezing or need to carry a bag that will barely fit in a 90L pack.

WM Bristlecone MF is wide cut -10F

Luc,
I appreciate the information. Unfortunately, nobody in my area carries the upper-end sleeping bags so I have to rely on online info to make an informed decision.
I sure don't want to carry a giant sleeping bag on my winter climbing trips, my WM Puma is big enough as it is!

I've got a sequoia bag -- it is pretty big, but it is also quite luxurious. I can't get comfy in a mummy, and it was a great purchase for me. Mine is overstuffed, which buys a few extra degrees.

If you buy from moosejaw, they have free shipping and free returns, I think.

Thanks Brian!
I forgot about the free return policy of Moosejaw(Backcountry also?)
That could certainly help.

So I found a WM Sequoia online on sale for 440 bucks. Pretty hard to say no to that! We'll see how it works and I thank everyone for their help.

Cheers!