You can add Garlington Insulators
below the SS foam pad and a space blanket between the pad and the hammock to get more range out of the SS system. You can use thinner underquilts too-- you just want to avoid compressing them. A poncho liner UQ would be a good candidate.
I use a SS clone that is also a poncho and the stock Hennessy foam pad with a space blanket. It works well, and is less expensive, light, and gives more protection from wind and rain. If you are into sub-freezing weather a lot, then I think the thicker down UQ's come into their own.