Ethernet Cables, do they make a difference?

On the LAN datatransfer is usually limited by the network cards of two connected devices. Most oF NAS do not support 1G.
If any of the devices in your LAN route from the storage of your audio file to your playing device is 100M - your entire connection is limited to 100M. Any cat5 cable will serve you as good as the most expensive cat6,7,8,9,10 whatever number you can come up with and willing to pay for.
Do yourself a favor and run a couple of tests:
1. Time one audio file copy over the cheapest network cable you have and compare it to the time of copy over the most expensive one. I bet they will be the SAME, and much less than duration of the audio track - conclusion: network is not a bottleneck.
2. Copy the same file file over to the playing device (computer or whatever) and compare playing it to playing from NAS. I bet you won’t be able to tell the difference.

Alternative approach - do the blind test and try to guess if cable is cat5 or cat<$$$>.

For strong believers: I’m selling cat13 network cables $111 per foot, custom made, special order... <Sarcasm>

Buy a Belden cat7 cable it has better bandwidth then a 6  thicker conductors and 2x shielding isolation.    They provide more wire to professionals than any body in the industry.
And they verify their results.

I went from a cheap cat5 Ethernet to a moderately priced Synergistic ethernet bought used (def the way to go). I had a 15-foot run and wanted to make sure I had good shielding and connectors for that length of cable exposure. I heard a small improvement- I interpreted as less shrill or grainy at the high end. For a couple hundred dollars I got perceived sound improvement and a cable that for sure is less susceptible to RMI RFI. So maybe piece of mind was all I got, but sometimes that’s all I need. 

A dealer explained that upgrading an Ethernet cable ONLY helps if you run it through a splitter box (any one will due). 

Ultimately, these things have to be tested with one’s ears. The guy who is content with just a lo-fi iPod should stick with that (even though even he would hear a difference when compared to hi-fi). 

I read all the controversies, then groked a solution for steaming MQA files ... relocate the DSL modem (80 Mbps service) directly next to my PS Audio Directsteam DAC then try various 1 meter ethernet cables.  

Started by drilling a 1/2" hole directly though the wall from inside my DSL wall box outside of my house and ran a 5 meter Blue Jean cat 6 cable directly to the modem.  Understand this DSL modem input cable is hardwired from the wall box using only 4 wires to a RJ11 connector (Phone plug) on the modem. Surprise, Surprise ... a noticeable improvement! Further improvement when I switched to a 4 wire individually shielded twisted pairs with 22 gauge silver plated solid copper wires. Even more when I used a 12V Lithium Ion battery to power the DSL modem. Crazy, fanatical ... I think not, just standard logic folks.

With the modem now optimized it's easy to hear the difference between the various ethernet cables when steaming MQA.  Hell it even sounds better when my wife streams her mp3 Classic FM radio station from London. I'm not kidding, the entire house fills with classical music, before it sounded like a mono car speaker.

I can easily state that optimizing your modem is equally as important as your choice of ethernet cable. 

I tried both a 15M Audioquest Cinnamon and Tera Grand Cat 7 cable from Amazon to connect my optimized DSL modem to the rest of house. Small but noticeable improvement over my Blue Jean Cable wired house. I suspect fiber optic is the way to go for whole house optimization but I won't be sending that kind of money.

If you are following my bouncing ball, for fun I compared the long runs of Tera Grand & Cinnamon between the modem and Directstream DAC ... nothing special. Diamonds rule on this short thoroughfare.