I don't like McAllister as Red John. Red John has showed to be a great planner and strategist.
This require a mastermind. Why McAllister was stuck being a sheriff?
Not impossible but very unlikely.
I'm not very fond of the Myer-Briggs typology of personality, but to explain in some way why I think McAllister doesn't fit like RJ, check his personality type, ISFJ, the guardian:
Red John could be a INTJ or ENTJ easily.
In great extent that's why Mashburn is my favorite suspect, check his personality type:
Strategist, planner, power-oriented, charismatic and leader.
Another interesting suspect is Bret Stiles, ENFP:
As a great strategist, Red John would never expose himself. He sent Timothy Carter in the end of the 3rd season.
tricked in the end of the fourth. Sent McAllister in he 6th?
He would never have a tattoo in any of his shoulders (that's for foot soldiers and a big risk).
He would never let choose to the enemy the place of meeting. Unless he revised it previously or had a counterplan. He let Jane choose the church.
If he was really in the list of suspects, he would eliminate Jane since it was a great risk.
How I see things Mashburn was in the Visualize farm (he said to Lisbon that was a problematic boy), he became the best student of Bret Stiles and even surpassed him, he got more money and success. And of course, created his own cult.
Stiles always knew who was Red John (once, he gave info to Jane).
Mashburn as Red John could be a sort of voyeur, that let his accomplices, possibly Carter and Stiles, make the killings.
So McAllister was the guardian and right arm of Mashburn ("I know many local sheriffs" said Mashburn to Lisbon).
So he sacrificed McAllister to Jane (RJ expected a countermove of course). The instructions to McAllister were to make mock of Jane ("I'm psychic") and ask for mercy (just like Red John victims).
What was the point? To make Jane a Red John disciple, the ultimate challenge for him, I guess. He gave to him revenge, and let to know the pleasures of killing without compassion (the perfect simmetry).
By the way, Mashburn fucked Lisbon first.
I was expecting a story line like this, it would be amazing.