[mcain]

What you typically do with lifelines is measure them, then get a rigging shop to make up the vinal-covered wires with swaged threaded studs on the ends. Then you have small turnbuckles and perhaps a gate. Most catalogs have the parts listed. I believe even West Marine would make them up for you. ABI has a nice gate shackle. While there are drawbacks, per the last post, this method has been used for years, and new lifelines should have several years'' service in them.
You can use the bare wire and nicropress--with the advantage of do-it-yourself. This is certainly as strong, but does not look as traditional.
Third way is to use some of the new, hi-tech ropes. Yale''s Crystalyne, New England Ropes'' V100 or T900 have amazing strength for the size. In fact, the same diameter as vinal-covered wire and the rope will be stronger. However, the splices are "core-to-core" splices and a bit of a challenge if you have never done them before. A local rigger might charge $12-15 for a splice, while a national outfit might charge 25-40. Or tie a knot. Check the specs on wire and the rope to get comparable strengths. I would guess 1/4 or 5/16 rope is probably more than enough. If I remember right, 3/8 T900 has a 10,800 load limit. Again, however, this does not look "traditional".
Just some thoughts. You pays your money and takes your choice......