Well the best laid plans of mice and men tend to turn to rubber when the cheese hits the road.
We ended up getting some much larger rope than originally anticipated as my buddy got a deal on some heavy duty rope from a local ski resort (for a chair lift; they use cable now not rope). This threw my line through a ring theory out the window as a) my rings were all way to small and b) this rope would have been a bear to splice around rings anyway as its pretty heavy duty and a bit over 1" across.. So onto plan B.
I tied turks head knots around the ends closest to the bar. The rope was stiff enough I had to beat these into submission with a 2x3 while loml pulled on the tail end to keep the knot from turning and I reefed the slack through and beat back the turns.
http://www.animatedknots.com/turkshead/index.php
and then back lashed the free ends using a variant of sheer lashing.
http://www.animatedknots.com/lashshear/index.php
The ends of the rope were whipped.
http://www.animatedknots.com/commonwhipping/index.php - I used the ashley form
The rest of the knots were a simpler Distel Hitch which still looks kind of cool. Once pulled taught this knot really doesn't want to slide up or down the post so you can literally stand on the rope and it won't even budge. I also had to beat these into submission with a club
http://www.animatedknots.com/distel/
Yes there is a wee bit of droop in the line, that's as tight we we could get it with two people pulling to tight and binding it off. It seems probable that it will droop over time as well, luckily the distal hitch is also fairly easy to undo so we can re-tension it pretty quickly. I was unhappy with the start of one side and re-tensioned it in about 15 minutes; although once the rope "sets" in place for a while might be harder.
Other than being a bit on the hot side for the first few hours you couldn't ask for a nicer place to spend the afternoon (it rained early and was somewhat sauna like for about 2 hours then the humidity dropped and the breeze came up making for a very nice afternoon).
Obligatory view of the mountain
And another view from the back porch.
edit: also if anyone knows of a use for 100+ wooden rings.. hehe.