Marmot Col Membrain for Denali trip

Looking at this bag for a Denali trip this summer. Has anyone used this bag before? I'm also looking a a WM Puma, MHW Ghost only b/c I can get a Prodeal on it, and a Marmot CVM Membrain as well. I have never purchased a negative degree bag before, have used Marmots and MHW bags through out Afghanistan sleeping in the sand, rocks, and dirt and they did great, but I know once it gets down to -20 and below you need to be able to be in your bag comfortable in case weather keeps you in, any experience would be extremely helpful thanks.

I've got a feathered friends peregrine I'd let go of. Not cheap but it's only been slept in 4 nights in the white mountains