Who knows if another will hold the line ...
The BT Business hub 2700HGV-C is one of the best on long lines and can hold the line down to around 0dB SNR - I have actually seen my 2700 running for quite a while with a negative SNR (< 0.0 dB).
Get a copy of Router Stats or Router Stats Lite and run that for 24 hours with samples every 30 seconds and monitor the SNR and sync speed. Then host the graphs on a suitable site and provide a link to them. From the graphs it is possible to suggest the best time to resync to get continuity of service at a good (not best) speed for the line. I played around with a line about 18 months back - the user was seeing frequent disconnects and then slow speeds ... Afterwards he was seeing a good speed ( lower than maximum) but it stayed synced for almost 30 days before we initiated a resync.
You are already exceeding expectations and many will find that a line of that length will not work at all.
You may also want to "protect" the modem by making sure there is nothing electronic or electrical close by, that it is as close to the master as possible and there is nothing electrical close to the path of the incoming 'phone wire.
M H C
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