Question Ethernet connection on 1 of 6 pc's 2x slower

Feb 9, 2023
I have an z490 mother board with possible speeds of over 2gbs. My internet speed is 1gb but not able to produce over 400 mbps download but capable for getting up to 40 upload
I have tried different ethernet cables still not getting anywhere to 1gb of speed. Tried the same ethernet on other computers and managed to get around 700+ download, 40 upload.
I also checked for most recent drivers and theyre up to date. What can possibly be going on? And have tried 3 different routers the speeds are still way less.
z490 e mother board
4090 msi
32gb ram
10900k cpu
Windows 10 Home
I would suspect software on the machine. A common one is any silly gaming network priority software or anything that talks about favor one kind of traffic over the other. A common one is called CFOSspeed. Anything like this you want to uninstall.

To see if it is windows doing it you could try a booting a linux image from a USB stick. These run completely from the USB and do not affect your window install. They are somewhat limited but most come with a browser installed so you can run normal speedtest.
You could also try a simple line mode program called IPERF. It should allow you to transfer data between machine in your house at over 900mbps in both directions. The program basically tests the hardware and the network drivers. Since it is a simple program it is not affect by thing like disk, memory or cpu usage.