Such a helpful response for others, I’ll ask for the latest model too. 
So my cunning plan is to migrate the two Hue hubs into the Hue Hub Pro, due out this week, so it runs on channel 25 nicely away from everything.
Then run up a factory wiped Home Assistant Green and run up a zigbee2MQTT on it using the newly vacated channel 20 - away from the existing Home Assistant zigbee2MQTT channel 11 and put it on a spare SMlight, I really like the SMLights.
Then migrate the reduced zigbee devices (54 currently 29/25 router/end) from the existing Home Assistant zigbee2MQTT onto the new Home Assistant Green zigbee2MQTT (which will use the main Home Assistant MQTT, which is on a massively over powered micro PC)
Then shut down the main Home Assistant zigbee2MQTT.
This new zigbee2MQTT will absolutely vanilla _ not that the last 5 zigbee2MQTT builds weren’t .
Then we can see how stable it is in a totally clean environment.
If over the next few months I will build back up with more powered devices and some switches.
The goal is to have it stable for months, ie no having to restart coordinator/ Home Assistant Green.
I will run it without updates to ensure they don’t interfere.
I am sure it can be done, if 2 Hue hubs can run zigbee devices solidly without hiccup or intervention for over 10 years I should be able to get a zigbee2MQTT running reliably for a couple of months 
Thank you all for engaging very much appreciated.
Printing up external enclosures for the 4 gates for Eufy entry sensors now that are due to be delivered today.
The Eufy door Window sensors have been great so far, with batteries that last 2 years and have run without any issue at all for 3 years.