The problem is that no one can really advise you on comfort! Of what you’ve listed, I’ve used the Circuit and the Helios, and FOR ME, hands down, the helios wins by a mile.
But I’m also 5’7″ with most of my height in my torso. Not sure the Helios can accommodate your torso (but please ask Katabatic – they are great to work with), but I’m pretty sure ULA has an extra small size (I think they even make kids packs??)
One of my really good hiking friends is pretty close to your height and uses the Arc Blast – she really likes her pack a lot (I can’t imagine it’s that comfortable, since the top sticks out like a FOOT over her head! But she likes it, and that’s what counts)
As for your comment on Cuben vs XPac on the Helios…I went with the cuben because I wanted to try it, and I’m pretty nice to my gear and rarely go bushwhacking. I have a custom made Zimmerbuilt pack made of XPac and I REALLY like that material. A LOT. I went back and forth about which to get in the Helios, and went with Cuben for no good reason at all (it is a cuben hybrid). I hope I don’t regret it, because it was an awfully expensive pack. We’ll see…….
I’m currently working on a pack of my own design that I want to sew – and it will be of Xpac.
I don’t envy your position – but know that everyone on your list has excellent return policies. So my recommendation is to pull out that credit card, buy a few and try them all on with all your gear…then see which one carries the best. Return the others.