Bruno Heller has specifically stated that he decided who RJ would be before they even started filming the show. This comment can probably be trusted more than some of his other ones, seeing as how he didn't have any reason to lie about that at the time, but he now has reasons to lie about who RJ really is, because we're only an episode away from the reveal, and he wants to keep the audience on their toes. So if we take this comment seriously, and we also assume that the list is correct, then we can conclude:
Gale Bertram
The most likely suspect of the alleged "remaining 3," but likely not RJ. Heller wouldn't plan out, from the beginning, for RJ to be the 3rd CBI director that appears in the 3rd season of the show. That doesn't make sense. He is, however, a probable suspect for RJ's right hand man in the CBI, and obviously a member of Tyger Tyger.
Bret Stiles:
Even though he was there since relatively the beginning, and it would make sense if Heller had planned him to be RJ from the beginning, he's much too old to be RJ himself, but very likely RJ's father. He has the unlimited resources that we expect RJ to have, and he has the ability to charm and manipulate others, but he likely taught that skill to his son, RJ, as Stiles is much too old to be RJ.
Ray Haffner
Fits everything a little too perfectly. The build, height, phobia, whistling, fondness for Lisbon... it's way too obvious. Plus, he seems as if he wants to help Lisbon + the members of her team more than harm them, which isn't how RJ would act. There isn't much that points him to even being connected to RJ, so my guess is that he's the guy that does any dirty work for Visualize. If he is connected to RJ, he's probably the "brute force" guy that gets the quick work done, i.e. killing the PI.
Reede Smith:
Doesn't make sense. He has too much of a temper, he's much too large to be RJ, and he acknowledges the fact that he's a "lower level guy". RJ is a showman, and if he was talking to someone he was about to kill, he would glorify himself in every way possible rather than saying he was a "lower level guy." He's probably a high-ranking member of Tyger Tyger that gets the brute force work done for them, and possibly RJ's main FBI informant.
Bob Kirkland
Dead. Definitely dead. But he may have talked to/left a clue for Patrick about RJ. His twin, Michael, on the other hand, is/was more than likely a RJ accomplice, if not RJ himself (provided he's alive). Some people are wondering "why did Bob kill Jason Cooper if he could identify RJ, since he's hunting him?" Well, the answer is, Bob didn't kill Cooper. Michael did. Watch the last scene of 5x18, when Kirkland and Jane are in the hospital. Jane is in Cooper's room, then Kirkland shows up and has some agents escort Jane out. Then, the shots change, and Kirkland has a different tie on. It very clearly switches from a solid red tie to a red tie striped with white and blue. Some time may have passed between those shots, we don't know. But then, Kirkland (likely Michael) goes into Cooper's room and asks him if he recognizes him. He's reassured and calm when Cooper responds with "no". He then begins injecting the poison into Cooper's IV drip, while doing it he says "It's okay, I'm here for you. I won't leave you." This could be Michael mocking what Bob said to him when they were young before Bob left Michael with their dad. Plus, according to Rosalind Harker, RJ smells of pine, nails, and earth. Michael Kirkland owns a large building in the middle of a pine forest.
I still don't think he's RJ though.
Thomas McAllister
He wouldn't be a bad RJ, and he has indeed been there since the beginning (1x02), but he seems to have a genuine desire to help Patrick catch RJ. If he were really RJ, he wouldn't want to help Patrick with catching himself, that wouldn't make any sense. Definitely a member of Tyger Tyger, but I don't think he's an accomplice of RJ.
Brett Partridge
He has been there literally from the beginning (1x01). His first line in the show is "Red John enters here". He appears to have acaraphobia, the fear of biting bugs. He fits the physical descriptions that we've been given from Rosalind + Sophie Miller. His voice is a match. He's the right age. He always suggests the opposite of the real case at a RJ crime scene. He seems loathsome and jealous of Patrick. He has a symbolic, between-the-lines connection to William Blake, the author of RJ's favorite poem, Tyger Tyger.
What better way to get your nemesis off your trail than fake your own death?
RJ: "I'm going to start killing again, often. Until you catch me, or I catch you."
RJ is Partridge, and he will most likely reveal himself in 6x08.
He's everybody's favorite creep, a ghoul.
He's irksome.
He's Red John.
