Wireworld Eclipse in general have a very nice warm smooth and mid-range centric sound. There somewhat lighter and more deficient on the bass vs other WW models. These traits seem to be characteristic of Ohno Continuous Cast Copper (OCC) that these models use, at least within Wireworld products though I've heard similar results with other cable co's that use this material.
Can't speak to such early versions such as the III & 5, but the change from the 6 to the 7 was in the insulation / dialetric material to "composilex 2". I can't remember exactly what composilex vs 2 was made of, but sonically the changes / improvements I heard were greater refinement, transparency and tighter bass. There's a review in Stereophile re: WW Equinox and Eclipse 7 that seems accurate to me based on my experience.
Would recommend you trying demoing WW Eclipse 7 from a dealer and hearing it for yourself. Just the improvements from 6 to 7 were quite worthwhile, so I imagine the changes from III or 5 are even greater.
