So the first (new) problem here is you are measuring your local network speed using a (variable) wireless connection to a server not on your local network, you also don’t say if you are using the same remote server in the app/on the site, they can and do vary significantly. The other thing is you are potentially limited by the WAN speed (broadband) and more importantly if you test when something else is using the connection (windows update, someone streaming, Sky box grabbing some OD content), not the WiFi connection. For example if one speedtest server has a great ping, but lousy bandwidth (I have one about 10miles away that falls into this trap), you get slow results, if another server manages is selected, ping increases slightly, but speed is my full broadband speed near enough, it’s better to test on the same server on both devices and ideally test 2-3 different servers to rule out server specific issues.
That brings us to the other big unknown here, routers tend to support two different wireless standards, 2.4Ghz and 5GHz. 2.4Ghz has better range and penetration (through walls etc) but is slower, 5GHz has faster speeds and lower range/penetration. If one device is using 5GHz and the other 2.4Ghz, you will likely get different results, Windows includes basic wireless status info, it’s worth checking what is being used and trying the other if the PS for example is using 2.4Ghz for example and the PC 5Ghz.
Finally the hardware/drivers, are you sure the antennae are properly connected and work? Have you tried altering the angle as even slight adjustments can help. I’ve not looked specifically at the board you mention, but generally drivers come from 3 sources, inbuilt/windows update, the OEM (Gigabyte), or the chipset manufacturer. That’s also the chronological order they tend to get updated, oldest to newest. It can be worth comparing how far out of date what you have is vs. the chipset manufacturer and if the release notes mention any specific issues that are resolved in later releases.