Have your line stats changed significantly since
these?
If not, the 8.3dB just shows that when they next increase the maximum sync allowed, you will be able to connect at more than the 79999/20000 shown there. Specifically, somewhere around the figures shown against "Attainable rate".
It has nothing to do with
this throughput problem, if you still have that.
See
this page for a description of how SNRM works, (your router is reporting SNRM, not SNR. Lots of makes do that

). Also see Section 3 on
this page. The same effect is happening on 80Mbps FTTC as described there for 8Mbps ADSL Max.
My broadband basic info/help site - www.robertos.me.uk
My domains,website and mail hosting - Tsohost.
Internet connection - Plusnet Value Fibre.
"Where talent is a dwarf, self-esteem is a giant." - Jean-Antoine Petit-Senn.
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