When you're done fiddling with pads (which WILL happen, eventually), check out the Jacks and their under quilts. They make the best. Period. Under quilts are the way to go when hammocking.
http://www.jacksrbetter.com/They are nice, but I'm a long time hammocker who hasn't bit on the the full on underquilt. I use pads. (just the blue wally world ones). I then extend my temperature range by adding a silponcho underneath my hammock as a windblock and insulation holder, and then putting in folded space blankets first, then if colder, cheap batting insulation. I get down
pretty darn cold (about -10C) with that, a good sleeping bag, and full fleece.
I'm not into an underquilt for three reasons:
1) they're expensive.
2) they are actually pretty heavy for what they are. my silponcho is multi-use, the insulation I carry even for cold weather is much lighter than an underquilt.
3) I can't go to ground in an underquilt, comfortably. If I end up having a place or two on my trip with no trees, or a beach I want to sleep on, with my current rig I can rig my tarp and sleep on the blue pad. I've certainly done that more than once!
If I end up trying to full-on WINTER hammock (and by winter I mean -30C - I migh get one.
As far as ratings and R values go? well, the R value you can
tell relatively, but realisticly, you have to see what *you* need in a hammock. I know what I need to sleep comfy, which may not work for you.. I do well down to about 5C in the hammock with just one 27 inch wide blue wally world pad. I get down to about freezing with the poncho added underneath the hammock bottom and nothing else. I've slept comfortably at -5C with three little mylar space blankets then added folded up between the hammock bottom and the poncho, and I've
spent a number of nights down to about -10 to -12C in a hammock adding about an inch and a half of cheap poly batt insulation from the sewing depeartment of wally world between the poncho and the hammock bottom.
