Donald, thanks for the info and your experience with the TNF bags. I'm filing that info away for possible future use. It's good to know that for some reason my Equinox is atypical for TNF bags.
Looking at the Fill Wt. for the TNF Fission, in my case, i don't think that I could get it down to 20deg F, perhaps others could. It has 25oz of PG Delta. My MB SSBB#3 has 25oz of Exceloft, but making up a bit for PG Delta's claim as being more thermally efficient (I'll accept that claim even having no comparative test data) is the fact that the MB bag is 2" shorter and can possibly have 1" less shoulder girth if the superstretch is relaxed. For me the MB SSBB#3 is a 30degF bag.
I bought on clearance, dirt cheap and couldn't pass it up, quite a while back a MtnHW Trekker (67" long), rated to 20degF, and it has 27oz of PG 3D - I've used this bag a lot and even new it was 25degF bag for me with just base and non-lofting mid layers.
I'm guessing that the two TNF bags you mentioned would be 30deg bags for me - not bad at all given their lighter weights than what I currently own and use for those temps. I'm impressed with your suggestions.
I didn't see any LOFT figures for TNF bags on their website, maybe I missed it? But if it truly has 5" (standard for a 20deg bag) of recovery loft (i.e. let's say 30minute recovery after stuffing into its sack), then I'll buy that it is a legitimate 20degF bag for an average to warm sleeper (not sure which, i.e. avg. or warm) with at least base layers on.
I sure do like the features in the one TNF bag I own and if someone can get them down to their Mfr Temp Rating, they are light wt. cp. to many of their competitors. The hood designs of the TNF bags (at least my Equinox which looks identical to some other TNF bags in hood appearance/shape) are great also, perhaps(???) only surpassed by Marmot hoods (just based upon reading other's experiences - I don't own any Marmot bags).
Appreciate you taking the time to make your earlier Post and share your personal experiences.