From Rick:
I spoke to the folks that make the Q-Powerline I use for kitesurfing today. They spent about half hour giving me all the pros and cons of various materials and structures of line.
They're willing to sell me some custom Q-Powerline that should be ideal for our application I would think. It's supposed to have a 700+ lb yield strength. It has an unbraided spectra core, with a very fine braid spectra sheath. The stretch is quite minimal, and it will be very supple compared to the normal Q-Powerline as they've agreed to skip the step of impregnating the braid. For our purposes, we should never come close to the life cycle of this stuff.
