I'm new to hanging and have been reading these forums for a month or so now, there is so much interesting info in here.
Anyway I was looking for the best suspension idea and reading so much about whoopie slings, UCRs, SLSs etc that it was sending me loopy, so I ended up with this Loopy Line Suspension idea (I don't think I've seen it anywhere). It is basically a single line of amsteel with three loops formed with constrictor splices.
Loopy Line Suspension.JPG
You could possibly use a Marlon spike hitch instead of a nacrabiner to attach to the tree huggers but I don't know how to tie them yet.
The third loop does have the same problem as UCRs in that a knot to brake the end of the constrictor, using the loop for this also keeps it out of the way.
I've only spent one night and many afternoons with this setup so far but have not had any slippage exept in the ridge line constricor when it wasn't braked and I touched it.
As there are two lengths of the rope for the entire length of the slings I suspect you could use a smaller rope (as long as it is not set up with too much tension in the ridge line).