We'll I swapped out my neighbour's BT HomeHub v1.5 for a 2wire Business Hub this evening and it was rather disappointing tbh. Router synced at 894kbps (to be expected given the unstable state of the DSL recently) but the 2wire's stats showed the SNR Margin as 5/6db. We monitored the stats for a couple of hours and saw about 3000 FEC errors and 250 CRCs. I'm no expert at interpreting these results but it seemed to me that with a sync of 894kbps the SNR margin should be higher if the line were good. Line attenuation was 63dB. By the way, the BT Homehub was retraining every 30 mins or so.
I checked all their internal wiring and it all looked OK but they have two extensions other than the BT master socket, with the router plugged in one of the extensions (not ideal) as there is no power near the master socket. They've used a star topology for their extension wiring with a link from the faceplate of the master to a junction box and then going out to the two extensions. The good news is that both extensions are fairly close to the master.
I removed the ring wire and replaced all the filters with new ADSL Nation devices. Only two devices plugged in - Router and a DECT phone (nothing in the master socket).
They are going to monitor the stats for a few days to see how it looks in terms of resyncs, FEC/CRCs etc.
Maybe time for a visit from a BT Broadband Boost engineer?