Ethernet Cables, do they make a difference?

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.

@billallen10  +1  and a helpful post. Thank you.

Did anyone do a blind test?
Please post your honest results.
It would be nice to see “placebo effect” eliminated.

Do not get me wrong, I love high quality network cables and connectors, but I make mine myself, use high quality cable and connectors and cut them to the length. Why? Because I can and it doesn’t cost me much. Otherwise I’d use cheap cat5, because there is no any network need in the house requiring network speed that cat5 cannot handle.