I think it must be Reede Smith. During Red John appearance in season 2, the actor Drew Powell was thinner. He now has short, straight hair and is a bit fat. He easily shows his anger, but Heller stated in an interview that RJ could be him with psychopathic anger masked by anger. That is the best way to hide it. Everyone believes that since he cannot hide his anger, he cannot be RJ as Rj is cool, calm but who knows Smith might be putting on an act as displaying his anger.