For music streaming, the speed of CAT 5e and up Ethernet cables should all be adequate and I doubt any speed differences would be audible. If differences are audible, my guess is they could result from shielding (STP) vs. no shielding (UTP), wire gauge, number of twists, termination quality, and possibly solid core vs. stranded wire. Here is an article that explains some of the differences from the perspective of audio uses and this article explains the differences between CAT 5, 6, 7, and 8. I find it interesting that many here stick with CAT5e or CAT6 Ethernet cables while the well-regarded Supra cable is CAT8 and SOtM’s highest level network cable is CAT7. Here is a listening comparison of different Ethernet cables by an audio reviewer.
