I personally think Red John is Haffner for a few reasons:
1. He is a creepy ass guy
2. When Lisbon asks him about the farm, he hesitates to answer (because it is already made aware that Haffner is a member of Visualized, and the way he says that he was a bad kid implies something).
3. Red John probably likes Lisbon, so he wouldn't kill her off right away (hence the smile on the face and an unconscious Lisbon). This also points out to the Hospital scene where Haffner comes a little too close.
If I'm wrong so be it, but trying to figure out a legitimate theory is really hard as there is a lot of info flowing through the show (People afraid of heights vs pigeons).
Btw I found something really interesting...
http://img.ibtimes.com/www/data/images/full/2012/11/27/323804.jpg
