Are you able to access the line stats in the router? In particular, the connection speed, attenuation and noise margin (SNRM) both down and up?
There is nothing special wrt speed about EO lines. Distance is the main determinant. Others are the quality and degradation of the cabling and junctions, and the presence of sources of electromagnetic noise between you and the exchange.
Do you have normal BT Openreach phone sockets, or are they the fancy "neat" MK type of built-in things that look more like hi-fi stuff?
Have a read of my Ring/bell wire, High noise margin and Miscellaneous nasties
section on this page
My broadband basic info/help site - www.robertos.me.uk
| Domains,site and mail hosting - Tsohost
Connection - Plusnet
UnLim Fibre (FTTC). Sync ~ 57.2/15.3Mbps @ 600m. - IPv4BQM
"Angels can fly because they can take themselves lightly."
- G K Chesterton.