Khorne Gallus would be the most violent and angriest creature, caring only about tearing and killing, before suffering in agony as it hunts for another target.
Nurgle Gallus would be very sad, forever drowsy in a blanket of sicknesses and infections.
Slaanesh Gallus would be the most unrealistic, stuck in its own fantasy world of unrelatable aesthetic.
Tzeentch Gallus would be very incomprehensible, squawking and vomiting fire from out of nowhere as a parody of the crowing it used to do when it was alive.