The first thing you need to do is to work out what the most extreme conditions you are likely to encounter are, and equip for that. If you think you might find yourself camping in 30 deg conditions then you might be best to get a 20deg setup as insurance. A full length UQ is good if you don't need to worry too much about weight or space. For me comfort is everything. I would rather go a bit bulkier and know I'm warm than to go minimal and have to improvise for extreme conditions I didn't prepare for.
I now use a Hammock Bliss Sky Bed which takes a fitted sleeping pad, so mostly an under quilt isn't needed, but you definitely need more insul on the bottom than the top in my experience. A woobie on it's own might be a bit thin for conditions where you need a 20 deg under quilt. I'd look at increasing the insulation on top. If you can afford a down under quilt, why not go the same with the top quilt? Maybe a 30 or 40 deg top quilt will be enough for any conditions you might be likely to find yourself in?
Just my 2c.
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