If you were going to get an underquilt for the widest possible usage (3 season - early spring to late fall) in the North East - think NY (Catskills, Harriman, Adirondacks) NH (Whites), NJ (Delaware Water Gap) - taking price and weight into consideration - used for backpacking, not car camping would the 3/4 Yeti or 20 degree 3/4 Phoenix be good choices? Could I get away with a 40 degree?
What might be some other vendors to consider taking price, quality, and weight into consideration.

I have a Mountain Hardware 15 degree down phantom bag that is my top insulation. I am 5'6" so I am pretty sure the 3/4 is fine for me.

Maybe I am being premature but I have been hanging around the house and testing the hammock with my Thermarest and it seems like a major PIA. I am going to Catskills in a couple of weeks and even though it is hot as hell in the NE now in the areas I am going it still drops to like 55 at night.

Thoughts?