The ethernet patch cord is the same as a Cat5 cable. Cat5e just allows for gigabit speeds, but you are nowhere near the capacity of Cat5 (100Mbits/s).
If only one of your client computers (wired, Dell) is the issue, then you should try to look into its' TCP/IP settings. What Operating system is that client computer running?
1) Download the TCP Optimizer from our main site:
https://www.speedguide.net/downloads.php
2) Start the Optimizer, and reset Winsock and TCP/IP: click on the "File" menu, choose "Reset TCP/IP", then "Reset Winsock", reboot the computer.
3) Start the Optimizer again, pick your advertised internet speed, and apply the "Optimal" settings.
Does that help?
If not, I'd run Malwarebytes and ADWcleaner. Is there some software running in the background taking up a lot of resources? (third-party antivirus software, etc.)
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