Switched over to the RJ11 provided with the Zyxel (which is about a meter shorter, but also much thinner) and it made a very small difference - ever so slightly better. I wasn't expecting any real difference, but I wanted to change the cable because my other one was a bit of a squeeze behind the router so thought might as well make a small note of it.
xdslctl info --stats
xdslctl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason: 0
Last initialization procedure status: 0
Max: Upstream rate = 61552 Kbps, Downstream rate = 338781 Kbps
Bearer: 0, Upstream rate = 50005 Kbps, Downstream rate = 330011 Kbps
Link Power State: L0
Mode: G.fast Annex A
TPS-TC: PTM Mode(0x0)
Trellis: U:ON /D:ON
Line Status: No Defect
Training Status: Showtime
Down Up
SNR (dB): 3.6 7.5
Attn(dB): 31.0 0.0
Pwr(dBm): 0.0 3.9
I have also attached a "crusty" image of VDSL2 overlayed (inverted) on G.fast HLog on my line. May be of interest to some, but really the attenuation just indicates 200m (which is about right). At least it falls off quite nicely from VDSL2 spectrum.