Doug and others, here's a point of reference.
Last week, I spent three night's in Wyoming's Red Desert and Wind Rivers hiking and packrafting.
Nights were 22 - 25 deg F.
I had the Cocoon Hoody, Cocoon Pants, and UL 180 Quilt.
The first night (25 deg F), I slept "comfortable but cool". I don't think my body had quite acclimated to the cold yet. It was also windy - a continuous wind blowing through my Wild Oasis tarp of about 5-10 mph, and I didn't have a bivy.
The second night (22 deg F), I slept "comfortable" and had a much better night's sleep. Same wind, but I had the tarp battened down to the ground.
The third night (24 deg F) with a little (2-3 mph) wind, and the tarp pitched "high", was great, and I slept "comfortable and warm".
Part of this increasing comfort comes from increasing nights out on the trail. I seldom sleep as cool later in a trip as I do on the first night. I really do believe that adaptive physiology plays a role.
I didn't have a bivy sack, which begs the question, how about a bivy + UL 60 quilt? I don't think that combo would have been as warm as the UL 180 quilt without the bivy
-- BUT --
The wind made such a big difference in my comfort on the first and second nights that I can't emphasize the importance of staying out of it when you sleep. These were not exactly big winds.
For *** me *** <== key point here
I think the Hoody+Pant+180 combo will be a pretty solid 20 degree system if I can stay out of the wind.
I haven't had the chance to take the Hoody+Pant+60 or +90 combo to its limits, so I won't venture to guess what the "temp rating for me" is going to be for that system. Doug, you seem to think it's somewhere near freezing. That may be accurate, but if I had to extrapolate my own experience, I'm going to say it's somewhere around the 32-40 range.