My Medium Ark Specialist in Pertex Quantum is 16oz which is Nunatak's stated weight.
My Large Ark Alpinist in Pertex Quantum is 23oz, which is 1oz over their spec's. Maybe I got a little extra fill by mistake?
I have not had my quilts long, but they seem to be very well made. The Pertex Quantum seems very fragile, so if your rough with gear, you may want to go with the heavier Epic Fabric.
I'd consider myself a cool sleeper, and I've been slightly chilled using the specialist. Not in the upper torso but in my legs, this was while wearing Capilene 3 bottoms as well.
I wore a Montbell Thermawrap Parka, so I was very warm up top. Night time temperature was probably 30 deg possibly, slightly lower.
This was sleeping in a TT Contrail as well, with a fairly stiff breeze, which I felt occasionally.(1st night)
On my 2nd night, I pitched the Contrail down tight, and then got major condensation, including on top of the quilt. So the extra condensation could had added to me becoming slightly chilled.
On both of these nights on the same trip, I actually didn't get chilled until very early in the morning, like 4-5:00am, and I also had to pee, which as most of you know, will chill ones body too.
I normally use a bivy with the quilts, when using a tarp, but for some silly reason, I thought the Contrail would hold a little more heat in, which didn't seem to be the case.
If your going to buy a quilt you might want to get a bivy as well, especially, if you plan to use a tarp too.
A bivy will help to block drafts, wind blown rain, condensation and trap more body heat as well.