...what DO "they" measure? What do any of the aftermarket guys measure? It's all done by ear? Again, given all the variables, what do they listen for?

Shielding is noise rejection as far as I am aware...straight wire with no gain...nothing added, nothing taken away. It seems as though just about every piece of gear has as it's basic premise, the unsullied passage of a signal's waveform...there are expectations as to the "traffic" and conditions it will encounter in it's travel...If the noise floor is limited by the active devices in the path, what do you expect to do, lower it further by use of a passive one, i.e. wire?

Shielded wire by design "shields"...there are special circumstances that require other designs...

Tensile strength? You may be able to take measurement or estimate a number, but there ARE other considerations, so it's not so simple...and it's use is not irrelevant in the overall equation...There's static and active...rope can haul, but it can be used for other purposes...loads are applied to the point of failure...bang! you get a number...climbing ropes are made specifically for that purpose, same type of load testing, sorta'...HOWEVER, climbing rope has a fixed number of times for which it can be used, how many times it can withstand the stretch/shock stress before it MUST be discarded as per the mfr....it is used for NO OTHER purpose during its active life...You surely would not use a hemp rope of similar load bearing properties in lieu of a certified climber's rope; hence some things ARE purpose specific. Other materials have burst strength, torsional loads, etc. all of which are specified and tested for known entities...as is shielding of cable. With wire, it's the ability to reject any change to the signal being carried...

jimHJJ(...unfortunately, gotta' go...tomorrow's another day...)