The full fix isn't just around the Hitron firmware. While that is part of it, the network end of the GRE tunnel terminates on equipment that also needed firmware updates I gather.
It is a combination of these things that contribute to the fix. As part of testing my GRE endpoint was moved to a trial area within the VMB network and even on the old Hitron firmware this resulted in a great improvement. So this could well be related to the fix and pave the way for the Hitron firmware to go beyond the trial.
Current performance:-
