Update - packet loss still an issue for me, varying from 3-10% according to my ping tests and the BQM. Gaming is sub-optimal currently, even on a wired connection. No speed issues.
As the issue doesn't appear to be going away, I'm including another BQM graph and a dump of my Superhub status. The Superhub figures are within 10-15 mins of a full restart.
Channel 4 and 11 stand out from the downstream - a lot of post RS errors and lower than expected SNR. Could this be what's causing the packet loss?
Worth noting that before my latest reboot, the RS errors were rather high after 24 hours of uptime. We're talking ~1000000000 on most channels for pre-RS and 4000-15000 post-RS (apart from 4 and 12 which were ~1000000000)