Ethernet cable type/speed discovery - router to PC.

Got Starlink last week and have had a few issues incorporating it into my home network. (Very slow)

In my problem solving, I had my laptop next to the router yesterday and connected various cables.
Starlink app is saying ~300mbps down.
WiFi - ~125mbps
Cat5 - ~30mbps
Cat6 - ~120mbps
Cat7 - ~250mbps.

I thought that was pretty interesting. Why would the wire Cat matter THAT much?

Aside from that, my problems surround the use of TP-Link wall plug adapters. Starlink just doesn't seem to play nice with them. I've used them for years on my previous ISP's and have worked well in my house, full speed wherever I put them. When plugged into Starlink they put out a max of 10mbps and totally fritz the wireless repeaters.
I am awaiting a TP Link Archer router to try and bypass the SL provided one. I'll definately use the Cat7 to connect those 2!