Since my previous tests had failed to leave me shivering, I decided to try my proposed "summer" (overnight low +35F to +45F) configuration.
Hennessy Hammock Ultralight Explorer (34.6 oz)
Hennessy Hammock UnderCover (9.8 oz)
Hennessy Hammock UnderPad (10.7 oz)
Jacks R Better Nest, used as top quilt (20.2 oz)
FlexAir pillow (small: 0.7 oz)
Evening temp was +28F, with an overnight low of +25F. There was a 30mph wind that was partly blocked, and it dropped to just a light breeze by 3am.
I wore the same clothing as in the +15F/+10F tests. I'll have to think a bit more about summer clothing because three layers is pretty heavy, but with the Micropuff weighing 13.2 oz and the closest other insulation being a 200-weight fleece vest at 13.4 oz, the Micropuff is still my lightest and most compressible upper-body insulation. I may leave out both the longjohns and the Cocoon pants, and wear my hiking pants to bed for leg warmth, but that will be a big reduction in lower-body insulation. Probably a reasonable risk for summer. (Maybe carry a ThinLight sit pad and put it under my hips at night if needed?)
I slept cold, but not shivery. The JRB Nest was warm enough, big enough, and comfy enough to keep my top-side warm all night. (Yay! That saves over a pound on the Ray-Way quilt, which I made heavier for winter use.) The bottom of my upper torso was cool, but the wind didn't seem to affect heat loss (I could hear the gusts but not feel them). The UnderPad wasn't long enough to cover both my feet and my head (bummer), so I made sure it covered my heels and relied on the FlexAir pillow, Bomber hat and balaclava to insulate my head (it felt sufficient). The worst cold spot was along the entry slit, which made my legs cold, and the discomfort interrupted my sleep. The UnderPad didn't seem to seal well there, and the UnderCover's entry slit is loose so maybe it doesn't hold the UnderPad close. I'm going to have to look at that area more closely with somebody in the hammock. I might need to add snaps or velcro to the UnderCover's entry slit edges.
There was moisture between the UnderPad and the UnderCover again, so clearly it is condensation against the non-breathable fabric. The UnderPad is open-cell foam, but it doesn't appear to actually get soaked; the condensation is on the outside. I staked the tarp down tightly against the hammock. This time there was some condensation on the tarp, and when the gusts rattled the tarp there was a light dusting of cold frost on my face (not unpleasant, though). At one point it felt very close in the hammock and I had a bit of a headache. I flapped the sides of the hammock to get some fresh air inside, and the headache went away. It's possible that the hammock was too closely sealed (the HH OverCover has a porthole in it to promote fresh air exchange). This could be dangerous, so I will make sure I don't stake it quite that close again.
Cold is acceptable; shivery is a bit on the edge. (When you wake up shivering, then stop and fall back asleep, are you warming up or dropping into profound hypothermia? That's a serious question to ask yourself in the middle of the night.) This configuration was meant to keep me cozy and warm at a typical +35F to +45F (which I will have to test in a few months), but it also needs to handle down to +25F. (I'm sure you've all heard the phrase, "Any day of the year..." It's happened to me more than once.) Not necessarily comfortably, but at least you shouldn't have to spend the night doing isometrics. This configuration passed the test.
I'm really surprised that this worked out. I expected to bail half-way through the night, but although I didn't get a good night's sleep, I was able to sleep most of the night. I thought about inserting the ThinLight at 3am, but I figured I wouldn't be carrying it in the summer anyway. Temps lower than +25F aren't likely in my summer hiking, and I figure the shiver point was about 10F lower. Thus, this configuration (4.75 pounds of shelter and sleep gear) should work for me for the full summer season in the high country.