I had a JRB Hudson River quilt which I liked, other than it being slightly narrow for me. I believe the JRB quilts are 48" wide where many of the Nunataks are 55". This makes a Big difference in warmth and cutting side drafts for me anyway.
IMO, The sewn in foot box of the Nunataks are warmer too. If I didn't have my JRB quilts footbox cinched tightly, I could feel cold air come into the foot area. Also, you have to assume the small cinched area is devoid of down, and can be a cold spot as well.
But, when using the JRB quilts in warmer conditions you have the option of leaving the foot end open to vent, where as with the Nunatak, I just pull me feet out, and either lay my feet over the top, or under, but not inside, depending on temps.
You also have the option of a sewn foot-box with the JRB, at no additional cost too, which is probably a better option for a ground sleeper, that never intends to use it with a Hammock.
Some nights I have to start out with the quilt just draped over me, then later as it gets colder, I need to get my feet inside, and wrap the quilt tighter around me.
But for the money, I think the JRB quilts are a better value, without the long wait as well. The width difference can be made up with the optional, add on wings they offer.
The only improvement I can see here, would for JRB to offer down filled wings.
You could leave the wings at home for warm trips, and bring them on trips, where you expect temps to be at or even slightly below the quilts rating.
Get busy guys!