if you can get speeds of 5/7mb then profile not stuck low and need to look for another cause hence why test socket to eliminate internal wiring
do you use an phone extension cable to reach master/test socket? is there any christmas lights near router which could cause interference?
congestion would normally be at peak times and be fairly constant not wide fluctuations - 0.5mb then within minutes jump to 7mb
I'm going to try one last thing to make sure it's not my wiring. I'll put the hub back on the test socket (although I imagine it's on the same wires as the master one as they're both on the first box as it comes into the house) and also try another ethernet cable. If it still doesn't get reasonable speeds then it's definitely not my end, unless there's a problem with the hub..
and without the phone extension cable
Latest test result.
That's with all new cables, hub directly into the test socket (on mine the faceplate is just an adapter that plugs directly into the test socket so the master socket is basically the same thing, but worth losing as much between me and the outside world as possible), just pc plugged in with new ethernet cable, no wifi devices.
test socketmaster should look like this