I was sent a sample of "double spring temper" 6 strand tightly twisted stainless steel wire by the Cablestrand salesman who sold me the original spool of seven strand. It was very nice of him. He's trying to sell more wire and help us out with something that will like prove much more durable. Anyway, it was enough to make up two sets of lines. Made one 59'6" and the other 59' even. It is amazing wire, and makes up easier than the regular stuff. Don't have the exact final price for sure, but it's a lot higher than regular seven strand. I am going to fly it next chance I get and see how it performs. It lays very straight, not tending to twist or kink, and seems much more flexible too. I can pull about an inch of stretch in a set of lines at about 20 pounds of pull. It's normally sold as medical wire, and is touted to be somewhat stronger than normal .015 seven strand stainless, which is 30#. I mic'd it the same diameter as the seven strand I bought, .0145. I examined it under a 100x microscope, and it still appeared smooth and evenly twisted.
Addendum: I made up some ends on the extra few feet left over and tested the cable with a pull scale I calibrated with some weights. I did nine different pull tests and it always broke between 21 and 24 pounds, only twice at the terminations. Going to fly it on some lighter models, and treat it like really good .012.