In reply to a post by Adduxi:

as I can't see a firmware update increasing CPU throughput.

firmware can do so if the writers decides to increase the cpu frequency

Ultimately the point would be to “offload” TCP processing away from the general CPU, so any uptick in CPU frequency would be of extremely limited benefit.

Quite frankly unless the firmware update unlocked some pre-existing capability, I am at a loss to see how this alone could provide significant improvements in performance.

Looks like this has been born out above.

Yes, the Router's Hardware Acceleration works absolutely fine for IPv4 as that was one of the selling points for this model. The CPU load hardly moves during speed testing on IPv4.
IPv6 obviously is CPU only, hence the poor performance in my testing.
But, hey ho, once I can drop dual wan I'll be looking for something better. I did ask one of the users over on the VM forums, who has moved to IDNet to test his Asus AX86U and it handles 1Gb IPv6 at full speed, so it is possible.

It’s not a particularly tall order to fulfil, so many relatively inexpensive routers will be able to do it.

A much harder (more hardware taxing) ask is decent VPN throughput for example.

Finally to put this to bed ...
Draytek eventually replied and said "IPv6 does not use any HA" So, it's is entirely CPU bound as I suspected. I did find out when tinkering, if I turned off all the DoS filters, it did improve a bit, maybe an extra 50Mb, but at a big risk.
So that's it in a nutshell. Topic closed.

They must've known that before they sent you the beta firmware 🤷‍♀️

In reply to a post by Pheasant:

They must've known that before they sent you the beta firmware 🤷‍♀️

Agree. It would have saved a lot of hassle had they just said it in the first place. !