In reply to:
You could be looking at 15-16Mbs after you move to O2 if there aren't any noise issues with your line and internal wiring problems. Your upstream attenuation does seem large though.
I did a bit of messing. For years I've run with modem plugged straight into a dedicated socket, no microfilter. Tried the O2 microfilter, which only has two wires to the socket (no bellwire connection). Attenuation instantly changed and synch increased.
Before:
DSL Type: G.992.5 annex A
Bandwidth (Up/Down) [kbps/kbps]: 957 / 11,298
Data Transferred (Sent/Received) [kB/kB]: 0.00 / 0.00
Output Power (Up/Down) [dBm]: 12.0 / 18.5
Line Attenuation (Up/Down) [dB]: 29.0 / 29.5
After:
DSL Type: G.992.5 annex A
Bandwidth (Up/Down) [kbps/kbps]: 1,334 / 18,540
Data Transferred (Sent/Received) [kB/kB]: 0.00 / 0.00
Output Power (Up/Down) [dBm]: 12.0 / 18.5
Line Attenuation (Up/Down) [dB]: 8.0 / 17.0
I'll try removing the bell-wire connections at the master socket end and see how things go.