Just my 2 cents - Seeing that you said you've had issues with Z-wave in the past, maybe dedicate one hub for only Z-wave devices and use the second hub for Zigbee and everything else. If you have rules and or integrations that only use the Z-wave devices, I'd keep those on the Z-wave hub. If you do this, don't forget to disable zigbee and Z-wave on the hub where they are not being used.
It would be prudent to try to diagnose the Z-wave issues you are having as well to try to remove he root cause of those issues
