I've been in the hunt for 100' of the round (versus flat) version of braided green and copper colored Polk "Cobra Cables".
Due to its braided design it is reported to have the absolute lowest inductance of any cable ever made. I guess this means it is the "fastest" cable ever made and yields the most extended high frequency response.
The wire also has incredibly high resistance which caused problems with solid state receivers/amps of that era. Cobra Cable was marketed in very long single run lengths and there are many stories about how lots of receivers and amps were "blown up" by this "horrible" cable.
The solution invented was to run 6 (or even 8) runs of the cable in parallel over the shortest distance possible to lower the resistance. The strands must be soldered green to green and copper to copper with care taken to never allow even 1 wild filament to stray. The insulation is supposedly toxic when burned so that presents another challenge.
At any rate, a fellow Polkie has been looking out for me and located 100' that I bought a few minutes ago.
There is one particular internet posting I've seen that compares paralleled Polk Cobras with $15K cables !!! Well, I'm going to find out. http://www.high-endaudio.com/RC-SpkrCab.html
I will be posting the project images and progress here.