For my runners, I always use single spectra slings tripled over, and I let them out when there might be rope drag. A friend of mine always uses the single/tripled system, but he uses tied perlon 6mm cord instead of spectra. He argues that on alpine climbs cord is more versatile for such things as v-threads, and retying slings for rap anchors in general. This sounds like a good justification to me, but I think that perlon is heavier, and significantly weaker than spectra. Perhaps spectra cord, or maxim tech cord are the best of both worlds? I would appreciate anyone's opinions on the subject.