I agree, 4.5 inch is -80 F using the formula
I don't know, maybe someone else has an opinion
What brand and model is your sleeping bag?
I was just looking at Nunatak Aplinist sleeping bag, randomly selected - 2.5 inches of loft, they say it's 20 F. The formula would say 0 F. Nunanatak is conservative, that's good. Aproximately consistent.
I have a sleeping bag that's 0.5 inch, I wear a vest that's 0.625 inch, plus a shirt and jacket that are maybe 0.25 inch, 1.375 inch total, 45 F according to the Ray formula, below about 40 F I start getting cold, so that's pretty consistent.