I have seen so many posts about this, I don't expect a good but perhaps some of my trial and error can help others.
I'm a systems engineer by trade, I have 20yrs of experience working in IT teams at a senior level, for a range of private enterprise size companies and currently I am an IT manager for a university. With that out of the way and now hopefully you are assured that I have tried just about everything - Virgin media routers appear to downshift the effective speed of ethernet links, while reporting a gigabit link at the switch.
*TLDR* If you are having this issue, please don't consider hurting yourself with sharpened RJ45's as I did, just buy a gigabit switch and use it as a core switch where all ethernet terminates for internet access. This will work, I can't tell you exactly why but I promise it will.
If you are here for the passion, the pain, the intrigue: I heard about this a long time ago and dismissed it as "bad cabling" "interference" or just general durpery. But a VM engineer once told me that the hubs rate limit traffic to ethernet. Whether this was to limit traffic and protect the network from bursts he didn't say, but he was adamant. I recently got called to a friends house, she's a gamer and notices lag where I only see smooth. So I was surprised when I tested the ethernet runs I put there about a year ago and only managed 100mbps effective speed, despite the remote devices (several different types) reporting a 1gbps link. I tried drivers. I tried manually setting to 1gbps full duplex to rule out negotiation issues, jumbo frames, I grabbed my fluke kit from the office and tested the runs, perfect. Gigabit, 20m length estimate, signal to noise all in the green tx and Rx pins.
Out of sheer desperation I grab a £10 Netgear prosafe switch and use that Infront of the router, it now being the only thing connected to the hub. Boom, instant fix, getting 900mbps effective speed and sub 1ms latency where it was 16ms even internally within the property. With all the tweaking I managed only 120mbps directly connected to the hub, but I technically made the network worse and it got 9x faster.
Now I cannot explain this, I thought maybe it was QoS tagging so I checked and tested that, nope.
The moral of the story is: cut your hub out of the equation as much as possible, and VM need to sort their stuff out so people can use that lovely expensive, fan assisted router 😂
If there are downshift to noise margins on the ethernet switch then the logic is bad, it would also presumably be causing a load on the router to achieve that, which can't be conducive to good performance. I came home and checked my LAN and reconfigured it to suit these learnings and it's been better - I used to get some weird latency on the AP's at the bottom of my garden, now they hit a switch before the router and internet it's gone.... Go figure 😂
