OK, thanks. Sounds like the tensile strength rating is probably more or less the same thing as the rope/webbing rating as used by Speer and HH. And that to allow for variables such as wear and knots, use 20% or so. So 5/32 with a rating of 1900 lbs ( which I think would exceed what HH uses) would give a working load of 380lbs per side. But are the effects of knots supposed to be in addition to the already reduced rating to 20%? The idea that you would then need to reduce that some more, to account for knots, would seem maybe a little excessive? That could drop 1900 lbs to only a couple of hundred. But if that was the case, a lot of HH ropes would be breaking.
Or bottom line, as Angrysparrow said, 5/32 works just fine.