I've been testing this for a number of days now.
I should say I've had a virgin engineer round too who added a noise suppressor and also replaced a section of cable which had multiple joins with one new length. This has no doubt improved things somewhat.
Ran opnsense for a couple of days and had one, maybe 2, instances of packet loss. Switched back to pfsense and things have improved, but still getting far too many spikes.
Disabling the bogon network check means I no longer get a complete loss of connectivity. Only a spike in ping and packet loss for about 15 seconds or so.
No conclusions yet, but a picture paints a thousand words.
Graph from yday (24th May) where I switch back to opnsense at 3.30pm:
This graph from today shows my switch back to opnsense yday at 3.30pm:
Clearly opnsense seems to be far, far better.