ethernet cable to stream from router?

CAT 5e or 6 is all you need for audio.

https://www.cablestogo.com/product/00810/3ft-cat6-snagless-shielded-stp-ethernet-network-patch-cable...

Supra CAT8 from seller zendada on eBay.  

As david_ten mentions Supra CAT8 is a good cable. It is the only "audiophile" ethernet cable I have used but the better sound between it and the supplied cable was easily noticed.

A two meter Supra CAT8+ cable purchased from eBay seller zendada is only $59 including free 2 day or so shipping. If you go this route be careful not to purchase the cable from the other seller. He is in England and you get hit with a $18 or so shipping cost and it takes about a month to receive it. Don’t ask how I know this. Incidentally, the cable being advertised as CAT8+ is a bit of marketing hype by zendada, it is really CAT8.

Supra CAT8 is another a good option.

I'm using Wireworld's Chroma 8.. Very happy with it.. Doubt you need their 2 more expensive ones..  A/B'd it with some generic cables and it wasn't close..