RCA Cable Quality

I've had MIT shogun RCA cables since the ninities  Can even remember what I payed for them But what I really like about them is their high quality locking banana connectors  They grib like nobody's business 

Same experience as OP. Tried a bunch (on loan from local hi-end shop), not an iota of difference. Same for speaker cables (AWG14 vs 5–6). So as long as it has mechanically decent connectors (e.g  Blue Jeans), I'm good. Speaker is bare wire, of course.

If someone questions quality of my components, look at my virtual system. Not stratospheric, but not entry-level either. So going from entry to something "better" has best shot to show *some* differences, but it doesn't. Tried it enough times not to bother anymore; remember definition of insanity.

As I mentioned before, differences in recording styles are MUCH greater, so "optimizing" cables is a fools errand. Or are the cable guys changing cables depending on which recording they play? LOL!

I think it is a fair point to acknowledge that things like cables and wire fall under the "law of diminishing returns"... I DO believe that there is something positive to be gained from almost any decent system by upgrading past the 'freebie' RCA interconnects that come with some equipment and the 'discount' bulk speaker wire towards products that are at least somewhat higher quality. I myself swapped out those cheapo free interconnects with some modestly priced (e.g., $20 each range) interconnects and absolutely noticed a reduced noise floor and especially a change in the signal from my turntable. I also upgraded speaker cabling from bulk 16 gauge to some SVS shielded 14 gauge and again, most notable difference was less background noise during quiet music passages, etc.

I also recognize that there is the POSSIBILITY of greater sonic differences  / performance when utilizing equipment that is more discerning (read that as "higher end") than the equipment I have. I also believe that it is entirely possible that noted differences above a certain threshold may be entirely listener bias and not anything measurably superior.

Lastly, I would add that any hearable difference likely decreases in both scope and range as you move up the cost ladder... and you likely will end up chasing truly almost intangible improvement with increasingly larger dollar purchases...

If your system is the same as you posted earlier thread... including a 1969 produced ITT GSX-500 tube receiver, and Fluence Turntable. Then it is probably the quality of your components that is presenting the challenges in hearing the differences in cables. You need a certain level of high resolution components before differences in cables become obvious. 

In the systems I have been assembling for the last fifty years the difference has been noticeable to jaw dropping depending on the components and overall system. 

Cables are like the ultimate audio conundrum.  If you can afford it and like playing around, you can do that, and I have no argument with it.  On the other hand, just being reasonable means sticking with a quality manufacturer with a good rep and a reasonable cost structure, then ensure the connectors are top quality and off you go.  Also, if you're using a MM cartridge, low capacitance would be nice, and mine are from Blue Jeans, "sound" great, and there you go.  This is a funny business, and a profitable one, it would seem if you look at how many manufacturers there are.  I'd stick with someone who's been around for a while.