Heres an interesting one.

My line stats:

Connection Speed 3712 kbps 448 kbps
Line Attenuation 34.0 db 19.5 db
Noise Margin 17.0 db 21 db

Never seem to be able to get above 4-5mbps, for any length of time.

Ideas anyone?

Just for completion purposes - tried removing extensions via BT test socket - same result
Added an I-plate (helped a bit, but only by upping it by an average of 200kbps.

Have a feeling its probably the target SNR, but not sure how to go about fixing this, currently with BT, but looking to swap soon. Possibly to LLU.

Thanks in advance.

Something wrong somewhere, but it's not the NM. You should be getting 8 Meg, even with that NM, which is being used to cap you down from 12 Meg.