Turns out that was a very bad idea.
Something is really messed up with 22.1 and my hardware.
I speedtest as expected on Opnsense (1260/900) but for some reason my downloads on the NAT side are like 200kb/sec.
If I use advanced DMZ on the HH3000 through to Opnsense then I seem to get expected speeds (940/940).
So it must be either something to do with the bxe module (unmodded gives same results) OR maybe it is the fact that the WAN is a VLAN. Either way it is unusable.... :-/