@jond as we both found out 'every day is a school day!'
I Was A Skeptic Now I'm Not So Sure
Well after being a luddite for many years and only listening to vinyl I have stepped my toes into the streaming world. I have bought a modest streaming setup consisting of a SoTM 200 Neo secondhand with a Topping E70 Velvet DAC, and I am pleased with the results for such a modest outlay in terms of streaming.
Moving to the point I was using a CAT 8 ethernet cable bought from Amazon thinking that as long as it's CAT 8 it will be fine.
On a whim and out of curiosity I bought a Supra CAT 8 Ethernet relatively cheap at £40. I was home demoing some Audio Solutions Figaro S2 speakers with my son assisting me, out of curiosity I decided to try the Supra Ethernet cable thinking that there is no way will it make any difference, fired up the same track we were just listening to, looked at each other and in near unison said well 'f' me, the music had filled out there was more tonal colour and what was a hint of brightness now became tonally smooth and musical.
In conclusion this has nothing to do with confirmation bias, it's what my son and I clearly heard and it was not just a marginal improvement.