This theory is based on the supposition that Patridge is dead, that assumption is to be hold until the next episode.

So, the reduced list comes to this (in order of plausibility):

6. Gale Bertram: although he is a really powerful man and kind of mysterious, he has not the psycho personality nor the intuition to be Red John, my theory about him is that he may have debts with Red John and is part of his informative crew.

5. Reese Smith: He is too compulsive and aggressive, contrary to Red John who is an "Artist, a Show man", he does not kill because of anger, he kills because of pride and enjoyment.

4. Thomas McAllister: The theory #4740 explains why he is not lower on this list, but we do not have anything on him, he just appeared in one episode and he was just a creppy cop.

2. Bret Stiles: He is with visualize which we know is pretty related to Red John's start (Red Barn episode), he has the intelligence, personality and charisma of a perfect Red John suspect. However, at his age he can not be Red John. But, he may be one of the main accomplices of Red John, he also has power inside the police (as we saw when he helped Patrick free Lorelei).

2 Bob Kirkland: It is clear he is deeply involved with RJ; he stole Jane's research, killed a RJ's friend to silence him, and has a rivalry with Patrick Jane, but he is far too obvious, and he is NOT cautious. I will say he is RJ right hand.

1. Ray Haffner: Raymond is like Jane; he has control of himself (and control others), he can be smooth and casual, he is a "member" of visualize and (probably) was at the barn when the first RJ murder occurred. He tried to take Lisbon, remember Lisbon has been a RJ target in many episodes, when RJ asked for a gift he asked for Lisbon, and now he took Lisbon to weaken Jane (I assume she is not dead and this is a plan to stop Jane)