This is primarily for Mac, but posting in case others are interested or care to chime in.
I've read about using IX quilts and the (baby) Orca in particular to buff up other quilts. I currently own two Baby Orcas & one insert (all IX), and have gotten pretty good results with them - love the weight and packability, although as noted elsewhere the fit needs to be a bit of Goldilocks for best results (not too tight, not too loose, edge seal matters).
I plan on doing some winter hanging this year, firmly in the 3/4 UQ category and will be going w/ down (Phoenix or Phincubator since I'm tall), but unsure if I should go for a 20 deg or a 0 deg, or perhaps 20 deg w/ bit of overfill (which is what I'm leaning towards).
I'm trying to get to just 2 UQ's that'll cover me in all conditions - double up when it's cold which will almost always be via car camping, use the down quilt when it's cold, vent the down as needed up to 45 or so, then Orca + insert up to mid 50's, then (vented) Orca for summer hanging. Also strongly considering a UQ protector, which I gather will add about 10 deg.
As I understand it, the issue w/ the Orca on the outside is compressing the down too much, but then if the IX is too loose I'm not sure it'll do much - but I've seen this recommended as the way to go. On the inside seems to make more sense to me, but I'm not sure how much extra warmth that'll give me. Would a Baby Orca inside a 20 deg down quilt bring it to 0? Would just the insert do it? Does it matter which is wider? Does there need to be any space between the Orca and the down quilt regardless of which is on the outside?
Any experienced opinions would be appreciated, thanks!