Interesting; I'm about 5'10" too, but find that with the 66" neo-air the heels of my feet hang off the end. Or I need a really beefy pillow setup to have my head hang over the other end. That's one place where the thickness of the neo-air sort of works against me, as with thinner pads I don't consider having the pillow on top of the pad.

My wife is slightly shorter than I, so we got the 66" version for her, but of course I did try it out. I can live with it, but prefer the 72" version. I expect that I could be fine with the torso length version too, just don't fully inflate or use backpack to avoid the "steep drop-off at the end" problem. I've not tried this, but am inclined at this point to stick with the size regular --- I'm not an ultralight backpacker.

At an ambient 20F outside, I definitely prefer a thin ccf pad on top of the neo-air, and possibly one below it as well. It's so tough doing an apples-to-apples comparison on this, however; it's not just variations in individual metabolism, but I suspect humidity, what it is that you're sleeping on (at an ambient 20F that could be snow, or dirt, or duff, or rock ...) and perhaps other factors.