loved your post... nice to watch your progress. i use the 'biner' system too. from jeff's warning, and after much thought, i upgraded from some cheap aluminum 300# biners to regular climbing ones. only a bit more weight, but a lot more peace of mind. you can also then clip that rig to the top daisy chain loop on a packstrap and use the tree huggers as thumb-loops (that was jeff's idea, not mine.)
i've got a 35* bag that i normally use as a quilt, but below about 55, i just get inside... i hate rolling over and getting that cold blast of air on my legs or back or wherever... different strokes for different folks i guess. works for you and me.
i too find about a 3*-5* difference in inside and outside temps. the closer the tarp is, the better it seems to be.
top of your sock works good for the stake dirt too