So, I`ve come with a new theory. If someone asks me who I think Red John is the first name that comes to my mind is Bret Partridge. Why? Well, mostly because of his voice, which is, actually, the only thing that could make us believe that he is RJ.
If I decide to think about it and examinate the evidences, like the CBI does, I might have a different opinion.
First, today I took another look on the 7 suspects list and I noticed something interesting: all of the suspects, except Bret Stiles, work with the police. So it seems like 6 of them have something in common, while Stiles has his own business and religion. Now, if you think about it, in the last episode of season 4, when Jane speaks with Red John in the limousine, RJ says that he found out about Lisbon and Rigsby not being dead when the FBI did. "I have a friend in the FBI", he said, so this could mean that he is not the one working for the police. For some reason, I generally trust in what Red John says to Jane.
Then, it is very strange for me the fact that Rosalind never said how old RJ is. Even if she is blind, and even if he used a disguise, the women slept with him, for God`s sake. It`s not very difficult to figure out how old is the man you`re having sex with. So why didn`t she mention his age? Is it because that would made a difference? Except for Bertran, McAllister and Stiles, the other 4 suspects are in their 40s, so if Roy would be older than 50, that would reduce the number of suspects at 3.
Least but not last, in the last episode of season 1, the one when Rosalind appears for the first time, the cop who is RJ`s accomplice, sherif Hardy, says that "Red John was a friend of his father". Sherif Hardy is at least 35 years old, so his father should have been at least 53-55 years if he were alive. This is why I can`t imagine Bret Partridge being friends with someone this old. I know it could be possible, but I just can`t imagine that.
So, in conclusion, my guess is Bret Stiles. Based on what I already said and on the other clues (he has intelligence, he is a mentalist, too, he has money, power, he is experienced, has his own religion, and seem the type of person who would listen to Bach, play the piano) I think that he is the son of a bitch. More than that, on season 4, he was trying to make Van Pelt join his Visualize club.
We already know that Red John has a thing for redheads, right?
The only thing that doesn`t fit is the voice, which I think is Bret Partridge`s. Of course, Red John is smart enough to put a different voice when talking to Jane, so this is not necessarily a clue.