Well I did a little testing last night, -18F down to -24F, no wind though. From 10pm to 6:30am it wasn't long enough to figure out what works, but it was long enough to learn some more and know what doesn't. It also occured to me that the clothing formula also depends on a persons size as well as sustainable activity levels. Anyhow it seems to work for me but I will now modify it so that only the insulation layers count, and the shells and boots and shelter are extra.

85F - Tmin [degF] = minimum clothing insulation weight, in ounces
e.g. 20F = 4 pounds, 5F = 5 pounds, -10F = 6 pounds