Add one more layer( a simple process) and it is a whole bunch warmer. Add one or two more and you are ready to approach zero or below. And no reason why you could not add more if needed.
IOW, instead of one 5 oz layer, use multiple 2.5 oz layers.
But when it warms up, take out all but the one layer for an almost UL approach. I am endlessly amazed how I can sleep most of the year here in the south with just one layer, and even freezing is probably covered with just 2 layers.
Though I can't say for certain about that do to lack of testing, because:
1: my other layers are not 2.5 oz, but closer to 3.8 oz/sq.yd CS
2: I have only taken the 2 layers to ~42, but was toasty and I feel I could have gone much lower
3: Have not tested 3 layers myself, but my son was very toasty using 3 layers mid 20s, so could have gone much lower
Anyway, that is one approach, though I have not seen any one take it. But that WB original CS UQ works real well and is super versatile.
( caution: the above advice is based on CS XP and what is probably Combat for the other layers. Have no knowledge bout if CS Apex would work the same)