After seeing that my wireless speeds were much faster than the speeds I was getting over Ethernet, I decided to invest in some new cables. I didn’t know it before, but I saw while I was changing them out that my current cables were Cat 5e. While putting my network together, I had just been grabbing whatever cables I could find in my scrap drawers. Now I have Cat 8 cables and my speeds jumped from 7MB/s to an average of over 40MB/s. It’s a much bigger improvement than I expected, especially for such a small investment.
Your connection is 40MB/s I assume
5e is capable of getting the full 1Gbps of my connection so I easily see over 90MB/s. That being said I bought a big 100m bulk years ago and have been clipping it myself with care.
If you were indeed using leftover/ free cables of cuestionable quality it indeed could be a reason for poor perfomance