As the C4 does not support the upcoming Protection Service's Radio migration, and the benefits of the zwave 700 radio in the C7, I would use the C7 for your device hub and the C4 for rules.
Edit:
As the C4 does not support the upcoming Protection Service's Radio migration, and the benefits of the zwave 700 radio in the C7, I would use the C7 for your device hub and the C4 for rules.
Edit: