Look like your line are getting 80Meg soon. On your stats increase 3Mbps per 1dB snr reduced
But you said...
I be very surprise a large jump from 70Mbps to 80Mbps for an extra 3dB lower snr if it has happen (I think stick to 73-74Mbps)
I did say that each 1dB is worth 3-4Mb on lines that make good use of the D3 band.
Any line syncing at 70Mb is making good use of the D3 band.
His sync increased by 3.3Mb with a 1dB drop in SNRM.
His line will reach 80Mb if it drops to 3dB.
You know better though
