A few thoughts that might be helpful:
The stiffness of carbon poles varies a lot. If an arrow shaft, it is called "spine," or the amount of deflection below level when the shaft is suspended over a 28 inch span and a weight a little under 2 pounds is lowered onto the center of the shaft. A shaft with more spine will tolerate a greater bend (smaller radius), but will deflect more in the wind. I guess the trick is to see how much deflection the whole pole (sum of the shafts) will tolerate before failure without too much deflection.
Roger, forgive the use of the word,"torque." My interest is finding some way to compare the relative strength of the shafts, and my thought was to use a "torque" wrench to measure the number of pounds of pressure needed to break the shaft. This would be with strong alloy tubing telescoped at least 2 inches over each end of the shaft, and maybe 12 or so inches of shaft exposed.
I would like to know which shafts are stronger before making the poles and subjecting them and myself to the elements, and would appreciate any thoghts on a simpler or better way to test them. I would also be remiss, Roger, if I didn't thank you for your very helpful and valuable articles and comments on this site.
About the inquiry about materials for ferrules (connecting inserts), the kite companies have pultruded carbon tubing available in many diameters. Determine the inner diameter of a carbon shaft, and you can order pultruded tubing to make the ferrules. Breathing and eye protection are vital when cutting the carbon. I use a mini-cut off saw with a thin steel blade purchased from one of the tool warehouses. Arrow suppliers also have saws with composite blades. The cut ferrules must be buffed smooth at the ends, with care later not to split the ends whenever assembling the poles. I have never had one of these ferrules fail, as they are thicker and stronger than the shafts. As pointed out many places on this site, they must be quite close in diameter to the shaft inner, or their ends will create a pressure point on the shaft inner.
I like Roger's approach also, using carbon shafts with a stiff spine, and prebent alloy tubing connectors at the corners. At least at one time, Fibraplex sold alloy connectors.
But I'm not ready to give up on flexing the carbon over an arc. Am also not keen on snapping expensive carbon tubes to see what it takes to break them. Have pretty well settled on the Easton Axis Nano shafts with a half inch spine, connected by pultruded carbon ferrules, and as earlier mentioned, may try a Carbon Express shaft also. The arcs will be around 43" high and quite long at the base. Will try a short one on Tarptent's Scarp 1 first for the center pole. Will let you know how it holds up here on Mount Chocorua in our regular spring gales. Should add that I tried carbon on a modified Mont-Bell Crescent 1, and due to the high degree of bend, much more than on most "dome" tents, I had many snaps whereas the DAC featherweights did not fail. Settled on a laminated carbon/alloy shaft purchased from Cabella's some years ago which is much stronger than carbon, but several ounces lighter than alloy for the whole pole, and had no failure (yet).