Absolute tosh. How many of BT's millions of customers do you think have Cat8 Ethernet?
Cat5e is perfectly capable of Gb speeds correctly wired.
Just to throw an Everest-sized spanner in the works (I've skimmed the thread and if this has been mentioned I missed it).
VPN connections are very computationally expensive, so on inferior hardware you are always going to see a massive slowdown when using a VPN compared to when not!
The CPU in the third-party router I use is several times more powerful than that in the Smart Hub 2 (assuming that it's the hub that is managing the VPN). VPN speed here maxes out at 600Mbps, and they don't even stay at that for long as the CPU in the router will start to throttle thanks to temperatures after some seconds.
Beyond a point, VPNs are going to kill your max speeds no matter what you do!
Hi, my vpn is on PC not Router so should not be an issue and to be honest recently BT appear to have stopped throttling my connection when on VPN so a policy might have changed