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.
Cat5e works fine for gigabit. If it’s not connecting at 1G, then the cable has been damaged and is probably connecting at 100M.
You should be seeing about 118MB/s in an iperf test on gigabit ethernet.