My experience was fairly similar a couple weeks ago I used a Ridgerest and a Thermarest guidelite 3/4 with my Western Mountaineering 10+ bag as a top quilt. Got down very close to freezing and it was plenty warm at times almost too warm.
I am guessing I could go close to 0 with that set up. I have used the WM bag down to -5 with no problem by itself but it would be very awkward to use the bag in the hammock. I do wish the pads were a little wider as every time I got a little gap between the pad and the sleeping bag I would get a cool spot. Simple enough to fix just shift or tuck the bag around like you mentioned.