Hi Carl,
I'm not much help here, I'm very sorry. I have only ever used moderately cheap speaker wire, multistrand, PVC insulation, very thick (little finger diameter all up), and have enjoyed excellent results.
Wire is like religion. Biwiring is good, works nicely, but beyond that I can't say. I'm a bit narrow minded; I know wire makes a difference, particularly silver plated copper which I avoid, but when I hear a problem I always go back to the design and fiddle with topologies and components. I'm not decrying the guys who know about wire, but I've got my hands full, so I'm open to suggestions!
Cheers,
Hugh