Wi-fi speed versus LAN speed

[CK31]

I'm looking for a bit of advice before I lose my mind!

Yes, I've already checked the Wi-Fi band I'm using. Yes, I've checked all the Wi-Fi settings. Yes, I've tested it standing right next to the router. I've worked through all the obvious troubleshooting steps.

We were upgraded to 500 Mbps fibre broadband recently. When I connect a device directly to the router via Ethernet, I'm seeing speeds of around 560 Mbps, so the broadband itself is clearly working as expected.

The problem is with Wi-Fi. On every wireless device in the house, no matter how close I am to the router, the maximum speed I can get is around 50-60 Mbps.

I genuinely can't work out what's going on. I've followed all the advice I can find about improving Wi-Fi performance and have tried everything I can think of, but nothing has made any difference.

Has anyone experienced anything similar or got any suggestions for what I might be missing? At the moment, it feels like I'm paying for 500 Mbps broadband but only getting a fraction of that over Wi-Fi.

[jamesn123]

@CK31 

Do you have any supporting screenshots to show testing methodology? 
E.g. What device you are testing on? What channel the router is currently using? What other routers nearby are using that channel? Is it using 2.4ghz or 5ghz as by default Sky routers mix those into one SSID and a device can jump between it. 

Do you have Sky Q at all?

Do you have any boosters or extenders?