Tough to diagnose game buffering/stuttering problem

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2. That's one of those...

That's one of those tough ones. Been there.

Does your CPU have the rating and number of cores for the kinds of games you play? Have you contacted the video card manufacturer or visited their forums to ask/find out?

All I can do is share what comes to mind and it could be way off base. Maybe you have tried them.

Run task manager and just make sure you don't have a huge list of processes running, if you see hundreds, then something is wrong. You can look up optimal settings for Windows that turn off unused processes and that might help. You said Win 10, but you didn't mention if it was Pro, which might be using processes you don't require. That can be looked up: Win 10 optimization.

Do try using a deep malware checker, if you can.

Also, what comes to mind is to check if you have automatic defragging turned on under the disk options. Turn that off.

I don't know if it still applies, (have not done gaming in a while) but are you using the Windows drivers for the video card and is there a dedicated one available from the manufacture? Updated drivers can often resolve glitches.

Also, have you updated your Wi-fi drivers using the manufactures version? Even though you tested the problem with a direct, Ethernet connection. Sometimes the drivers are from the same manufacture.

That's all I can think of off hand. They might all be wrong. You know how it goes.