Seeing where you are:
Go for the lower-temp model, unless you hike exclusively in the summer.
Why? Because if this hammocking thing works for you, the seasons for being in the woods and on the trails are extended into cooler weather and rainier / muddier conditions. You camp above the muck and damp, and can be enjoying shoulder seasons many ground-campers avoid because of the mess. And cooler weather of early Spring and late Fall or winter encourages in me higher levels of effort w/o hassle of dehydration.
The weight, $, and bulk difference in UQs is small, and you are in a geographic area where the real temp can be 15F lower than the forecast.
I would not say the same about a 0F UQ or about over-stuffing. They both take me over a limit in bulk, all for rare, rare conditions for me, where wind is a greater issue for heat loss than temp.
I agree. I will have a broader temp range. I just have to find a 5 oz savings somewhere which shouldn't be hard.
Spoke with Leigh back and forth and she suggests a 1 oz overstuffing on the 30 degree UQ to belay my concerns. I think this may be the best of both worlds for the temps I will be in so I am ordering it. I will be heading out for a backpacking trip in a couple weeks and I will let you know how it works for me.