Hi,
The Cally Cally tends to grow even bigger than Faramir's H.Thoracatum (up to 8" I believe). They are indeed well armoured and can put up with a fair degree of aggression. However I am not familiar with Green (or any other kind of) Sunfish and their behaviour. All these Armoured Catfish are peaceful and fairly slow moving. They do not hit back if attacked like a Synodontis, Dora, Plec or Loach might. They also tend to be active in the day and unlike many other catfish rarely try to hide away.
So they will often be in the line of sight of the Sunfish. If these are the kind of fish that will constantly harras other fish then your Armoured Cat will get stressed. It will be defenceless and although it may not take much physical damage from each attack if it is constant the Cat may die from some stress induced illness.