How would the armour of Hood's planned sisters differ from hers?
Short answerThey would be better protected and closer to fast battleships, but their cruiser-style subdivision would still keep them on the battlecruiser side.
NotesHood is an early step from the battlecruiser toward the fast battleship. Her planned sisters improve the armour scheme, and the G3 design advances farther along the same path. Both remain battlecruisers because their internal subdivision stays closer to cruiser practice. A true fast battleship sacrifices some possible speed for armour, battleship-grade compartmentation and greater survivability.