Help with a down bag choice

What about the WM Caribou? Highlight with full zipper, robust fabric, room for layering, but slightly heavier.

Already have a summerlite but looking more for something super light like sub 16 oz or under.

For a 40 degree bag, are you really sure you want a down hood? I would prefer no hood in a 40 degree bag for sure. A light beanie will always be enough for my head at 40 degrees or above. Most times I would use a 40 degree bag, I would probably not even need a light beanie. Then the Zpacks bag would be great.
Also, are you sure you need a zipper in a 40 degree bag? With warm temperatures, a small amount of draft is usually no big deal. At 40 degrees, a zipperless quilt is a great option. Then you can look at Enlightened Equipment or various others. And you'll be saving a fair amount of weight.

Setting up an AT thru hammock pack.

Really want something with a hood, and I will also be carrying an Insultex liner just in case I need more warmth.

Plan to Start out early and for that I will also carry a climashield topper quilt then as it warms up will ship that climashield topper home leaving me with a SUL 40dF bag and an IX liner.

I will have a pad of some sort so if I get stuck in a shelter I will have some bottom insulation and also if it gets too cold I can always go to the ground/shelter and use the 40dF bag, IX liner and UQ on top for more warmth.

At least that is my thinking for now.

I do have a down hood and a Zpacks bag is high on the list due to weight.

Also what would probably serve me best would be a sleeping bag with continuous
baffles so I could shake the down around, for hot cold etc. At least I think Zpack bags have continuous baffles and if so I would probalby go to a 30dF bag since you can shift the down around. 30dF cont baffle bag I would probably skip the IX liner.

For temps above 20 deg, I love the combination of a down quilt and a separate down hood. I'm a left, right, back sleeper and the down hood moves with me as I move under the quilt.

Yes I am probably going to go that route

If you are open to the quilt route, I can't recommend enough the Katabatic Chisos. Under 16oz (14.6oz w/900 fill IIRC) and conservatively rated at 40f.

I like my down hood when I go to sleep, its like having a furnace around my head. After a few hrs I usually have to take it off unless its really cold, my head sweats. A bag is actually more comfortable , the hood is more like the temp in the bag. Temps where a beanie isn't enough, but the hood is too much are aggravating.unless I have fleece goody, then hoody and beanie are a good combo.

I have an overstuffed ($40. extra) WM Megalite and love it.

BUT… if I were to get another down bag I'd get one with DWR treated down like Down Tech to Dri-Down.
Sierra Designs 3 season bag was highly rated by those communists at Backpacker magazine, for what it's worth.