Value of a premium Ethernet cable

Value Sonically:  ZERO. CAT-3 will do just fine. You almost can't get it so CAT-5 or 5+.  CAT 6 is what was 5+. 7 or 8 are marketing BS)  5+ has a specific bonding between pairs to keep their impedance consistent for 10G. Do you need 10G for audio?   Ethernet it packet based. Errors are fixed in the IP stack. Magic is not needed. 

Value for placebo satisfaction: Very high to some. If you believe, go for it. If it is real to you, great. 

Value for the economy: Makes someone else a lot of money and uses up what you should spend on speakers. 

Side note:    The ONLY cables that are in fact directional are either balanced cables with a isolated shield/cap bypass which can be used as a band aid for ground loop problems, or pure snake oil.  Directional? Audio is AC!

A shield connected on one end without a bypass cap is called an "antenna."  You could help yourself and invest in a little time taking an on-line free course in basic electronics. 

Many single ended cables are in fact, snake oil.  I can't separate reality from belief, you will have to do that yourself. 

Extraordinary claims need extraordinary proof.  If something does not follow the laws of physics in this universe, I suggest extraordinary claims are required. 

Bad engineering and advertising does not solve other bad engineering.  Maybe you can avoid hum be reducing the ground paths, but the shield is no longer a shield and you now are subject to interference.  This is why correctly designed cables have a bypass cap connecting the shield to complete the circuit for RF but not for hum.    We learn these things in first semester electronics. 

The part I can agree with is "try it yourself at home"

If you think you are getting noise into your analog system via the Ethernet, I suggest you have a crappy Ethernet NIC so you are expecting magic cables to fix a bad design.  If you tested you would probably find a lot more garbage is from the processors in the router and switches and not RFI. If your receiving device does not take care of it, it was not correctly designed to work in the intended environment. Blame your box, not the cable.  As far as which cable it is possible to transfer this noise, it is only the last link as the signal is reconstructed in the router and any switch. 

If you believe, so be it. 

What you hear is what your brain says, not the actual sound.  -140dB noise flor? Well that is truly fantastic so quite a great system. Not sure how you get that as even a Bryston amp has about a 114 dB SNR. -140 is pushing Johnson noise. With what source material? A CD with 110 dB dynamic range compressed to maybe 40 to make it loud?   A super great LP direct to disk that maybe has 65dB?  Or do you have some first generation  24/192  digital files before mastering?  I bet what you are actually hearing is more like -80 dB if it is actual physical, not perceived. 

Oh, yea, guess I'd agree a lot of big box cables and hubs are junk. So junky I only get 360 Mbs on my computer with Amazon cable, self terminations, Netgear dumb hubs and the supplied Spectrum router and Modem.    Not saying Belden is the only or the best but if you buy their wire, it will meet spec.  I have had no problems with Netgear hubs.  Instead of expensive linear supplies, I just put a ferrite on the wall wart cable. 

No one has eluded because in truth, CAT-3 is more than what is needed.  This is just another "reaching for magic" topic by well meaning folks who do not understand how Ethernet works.  That extends to a lot of equipment makers apparently. 

Cost has come down, so no harm in running 6a if it makes you feel good and future proofs you. 

I encourage folks here to do a little research on their own and understand how Ethernet works and how the IP stack works.  As one member suggests, GOOGLE can be your friend.  Things work the way they do, not by some made up rules because someone wants them to work differently. 

Folks  may also be interested in the iFi "better" wall warts if you think switch power noise is causing you an issue.