When I was on ADSL2+, for a while I ran with a connection-time noise margin of 0.3dB. At that level it matters . Also at higher levels, as the use of it and the Synergy 2000 system and this one both drop(ped) the noise margin by 0.4dB when used.

Hi.
Is there any disadvantage to running at that low level?
I have a very stable line that doesn't vary by more than .1db or so.

I currently run at 3db but have thought about pushing that right down to 1db.

There could be a problem if you are on Fast Path. I was on Interleaved and found the FECs went up quite a bit, but that didn't matter as the throughput wasn't affected. On Fast Path it would cause re-transmissions and possibly defeat the object.

The other considerations were that basically I don't do streaming, (on the few occasions I used iPlayer I didn't do this), so a few disconnections in the evening didn't bother me, as my 24-hr variation was 2-3dB, and on LLU I didn't have a DLM to worry about slugging the line because of instability.

Even with evening disconnections, my lowest sync remained considerably higher than if I used 3-4dB sync-time margin to avoid them. Any intermediate setting was pointless, as the inevitable reconnection(s) were at a higher margin so a lower sync. (If you follow that logic).

A good compromise for you may be to sync at 1dB or lower well into night-time.

Thanks.
I'm on fast path and LLU, no DLM.
I'll give it a go, keep an eye on the error rate and see if I can manage to get any increase in real world performance.