Noise margin is entirely independent of distance. It is a function of the quality of your line not quantity (length). However, the longer your line the more scope for problems.
As the max attainable is in excess of the USO , then it could be that your line can be made USO compliant, have you a regular NTE5 master socket and tried from the test port ?
If their is a 3/4/5G mobile service capable of 10 Mb where you are then that would also satisfy the USO, it’s not necessarily the case that OR will be doing anything , unless your line has a defect and needs repair, that in itself could get your sync speed over 10Mb ( as you have a max attainable of 13Mb, that doesn’t seem overly optimistic )
With the front plate of the socket removed and a brand new BT issue ADSL filter plugged directly into the master socket, the router syncs at 10.000Mbps today.
Is that one off aschievment enough to let OR say that they have satisfied their USO obligation, or there any expectation that the line will provide service like that with any reliability?
As can be seen from my router's log over the past few days, 10Mbps is rarely achieved, in fact the line spends more time out of action than syncing at 10Mbps
if now connecting at 10mb can you post hub stats please
your noise margin is 9db so if you just maintain connection I would expect that to drop to 6db with your speed increasing nearer your attainable - but needs to be stable - no drops/resets