After "Red John's Rules" (S5E22), I really wish RJ turns out to be directed by Sean Barlow with Ray Haffner, Brett Partridge, and Sheriff McAllister committing the RJ murders.

Sean Barlow is the friend/business partner and later enemy of Alex Jane, PJ's father.  Other than Bret Stiles, SB is the only character with the charisma, brains, ruthlessness, psychic/mentalist skills, organization (see below), and showmanship to carry it off.  I realize this is highly unlikely...  The others--especially the list of 7--are either too obvious or lack credibility by comparison.  (Bret Stiles is the obvious alternative, but is too old.  He also doesn't seem depraved enough to personally revel in RJ's heinous murders.  He seemed genuinely upset at the murder of the female Visualize member who worked on his security team.)

The following was established In "Red John's Rules."  Long with the carnival, SB would know PJ's past, including Eileen Barlow Turner (who SB raised and who RJ murdered), the Carson Springs carny layover location, and possibly Gottleib, the director of the Child Protective Sevices and a RJ friend.  Becoming an enemy of Alex Jane and given to nursing grudges and swearing vengeance, it is likely SB would have pursued vengeance against Alex Jane and his family, PJ.  (As Judge Dellinger in "Red Dawn" S5E5 said, "If you want to hurt a man, don't kill him--kill his family.")  According to PJ's carny friend, Pete Turner, SB is ruthless and capable of killing his niece Eileen.  Since SB and Eileen were with the carnival, he might well know of PJ's "happy childhood memory" first-hand by simple observation.  If not, SB would have had access to the young PJ and, as a psychic and mentalist himself, could have used hypnosis.  Finally, SB maintains connections with Ireland.  He is old enough to have had those connections in the days of the Irish Republican Army.  The criminal/terrorist network that used to fund the IRA is still accused of being involved with bank robbery, extortion, smuggling, and counterfeiting.  Were SB involved, that would give him a criminal network with international reach and connections to other criminal/terrorist groups.  In the past, the IRA was involved with the PLO, Quadafi's Libya, FARC in Colombia, and the Basque ETA.  As part of an international criminal network, SB would naturally come in contact with disturbed and/or criminal men, and would have opportunities to identify and recruit allies in police departments, the CBI, the FBI, and Homeland Security.  So SB would have the personal traits plus the organization and resources to do many of the things RJ does--murder, favors for friends, infiltrate law enforcement organizations, and pursue vengeance for decades.

As for PJ and RJ, Sean Barlow could personally commit the RJ murders.  But I think it more likely he is the brains of what is now the RJ criminal organization, with others doing the actual murders.  Ray Haffner, a self-admitted "troubled kid," would be my guess for committing the RJ-style murders at the Red Barn farm 25 years ago ("The Red Barn," S5E13).  The murders are now done by a group of similarly-twisted men--perhaps, Brett Partridge and Sheriff Thomas McAllister as well as Haffner.  Why Haffner?  He is the right age to be at the farm.  His height, build, age and hair are credible relative to Rosalind Harker's description.  Haffner has extensive links to relevant organizations--former FBI agent, former CBI Senior Agent, and past/current Visualize member (Red Barn farm link).  His background in surveillance would equip him to access various computer networks and spy on those pursuing RJ.  So Haffner could have murdered PJ's family in reaction to his TV comments about RJ.  Knowing PJ was likely to become a prominent psychic, SB could easily predict PJ would work with police and comment on famous killers for the publicity--thereby securing the vengeance SB swore to exact.  The SB-Alex Jane-PJ-RJ connection thus comes full circle.  Note that tormenting PJ is personal for SB, too.

The lurid RJ murders stand out, but there are also ordinary crimes.  Todd Johnson ("Red Moon," S3E9), the RJ friend and EMT serial cop-killer, may have killed some people for reasons, not just arbitrarily.  Todd Johnson's archaeologist friend Montero ("Red Queen," S3,E16) was a gun-runner to Central/South America for terrorists and dictators (FARC in Colombia?).  Finally, Bosco's team was working on an international drug cartel case when Rebecca murdered them at RJ's direction ("His Red Right Hand," S2E8).  Yes, RJ wanted PJ back on his case, but there could have been a monetary interest in disrupting the drug cartel investigation as well.

Connecting RJ to ordinary crime as well as psychopathic murders provides the resources for his activities and links to other criminal and terrorist organizations, domestic and international.  That could provide a legitimate reason Homeland Security and the FBI to be interested in RJ.  Gale Bertram and Bob Kirkland could be working together for legitimate law enforcement reasons.  Kirkland asked Bertram whether "we" could trust Lisbon.  If they were RJ friends, why would they ever think they could trust Lisbon?  Conversely, if they are working on a legitimate investigation, that comment might make sense in that they are concerned with PJ being compromised by Lorelei ("There Will Be Blood," S5E16).  (BTW, I find it intriguing that Bertram has a plaque for bravery in his office ("Strawberries and Cream," S3E23).  That seems incompatible with him being RJ.)  If Homeland Security and the FBI are investigating several international criminal/terrorist organizations, they may have split it into several smaller investigations to protect the larger effort from being betrayed by one leak or one bad agent.  Kirkland's interest in Lorelei and his act of killing Lennon could have been motivated by protecting the larger investigation (shaky, but ...).

The Mentalist would be well-served by broadening it beyond just RJ and the CBI murder-of-the-week, especially if (the main) RJ is caught in season 6.  I personally would like to see Bertram gone (killed being brave?!), Lisbon promoted to his position, Cho promoted to unit head, and Jane occasionally working with the FBI and Homeland Security on international criminal/terrorist cases.  With all that change, PJ and Lisbon could pursue a personal relationship (Jisbon) while preserving enough change and tension to keep the series new and interesting.  Like I said, unlikely but interesting to speculate.

If you got this far, thanks for spending the time to read all this! 

o  Thomas McAllister - The character is simply creepy.  The fact that he isn't obvious would make it interesting.  (See below for why I ruled out the other 6.)

BTW, I was hoping S6 would be painted on a larger canvas.  Perhaps, RJ and friends could be one tentacle of an international terror/crime network.  That could explain the Homeland Security and FBI's interest in RJ.  Montero--Todd Johnson's friend (a known friend of RJ and serial cop killer)--was a gun-runner serving South/Central American terrorists and/or dictators.  RJ's slaughter of Bosco's team presumably disrupted the investigation of a major, international drug cartel.

Why I ruled out the other 6 RJ suspects:
o  Bob Kirkland - Several S5 shows provided lots of clues that Kirkland could be RJ.  Disappointingly obvious if Heller chose him.  He also comes across as weird and secretive more than evil.
o  Gale Bertram - Bertram was not nervous (per PJ) at the mall before PJ killed Timothy Carter (S3 finale).  Bertram had a plaque for bravery in his office, shown in one Strawberries and Cream episode (S3 finale).  Seems unlikely were he RJ.  He also has little hair--unlike the description of RJ's (blind) mistress, Rosalind Harker.
o  Brett Partridge - Too obvious.  Creepy, yes, but zero charisma. 
o  Ray Haffner - Could be, but he doesn't seem intelligent or evil enough.
o  Bret Stiles - He has the charisma, intelligence and organization.  But he is rather obvious.  He also seems too old.
o  Reede Smith - Could be, but he is too heavy to match Rosalind Harker's description.  So far, he has not been portrayed as intelligent or charismatic enough to be RJ.

. and Brett Partridge seem way too obvious.  The season 5 shows   They would be a let-down.  Bret Stiles seems too old.  Ray Haffner just didn't seem to have the charisma or intelligence.  And Reede Smith does not fit Rosalind Harker's physical description.