I think Partridge is RJ and here are my thoughts on this and Stiles and tiger tiger.

1. I think RJ is or at least used to be very close to Brett Stiles. Perhaps Stiles helped him in some way as a kid (like the way he helped the Ecuador guy who became minister). I think it's possible that RJ is completely obsessed with Stiles and wants to be noticed by him. He's probably jealous of the control he has over people and how so many people worship him. He wants to be like Stiles - adored, worshipped and a performer.

2. I think RJ tipped off the FBI about Stiles in order to get him out of PJ's way. He either wanted Stiles arrested and safely in custody or he knew Stiles would run and find refuge somewhere. He either cares about Stiles a lot or he wants Stiles alive so that he can find out he is Red John and be "proud" of him.

3. I think Stiles suspects Partridge is RJ but doesn't know for sure. That's why Stiles was so surprised when PJ said that RJ was one of the 5 in the room. I think he was actually really happy that Partridge wasn't there because now he believes his suspicions about him being RJ were false.

4. RJ has led Patrick all this way, being in control and he has timed this whole thing so that it is revealed now because Stiles has cancer! It's important for RJ to reveal himself before Stiles dies!

5. The tiger tiger thing is a complete red herring. RJ is trying to frame one of them. This could just be convenient for him but I think it's more likely that the tiger tiger crew were involved somehow in a murder cover-up of some sort with someone (or more) RJ was close to. This could have been a trigger for his killings or simply added fuel.

6. Partridge's first line in the show was "Red John enters here". That is fantastic.

7. Partridges aren't fond of heights.

8. I am almost certain there is a link between Stiles liking Van Pelt & her red hair, and RJ having a relationship with a redhead (Rosalind Harker). Maybe RJ is Stiles' son and they have similar taste in women.

Some of these things don't directly point to Partridge but I think it is the most likely scenario. Even if we disregard the fact that they both have the same voice, he is the one most like a performer, an artist and he always seemed a bit creepy, a "ghoul" and a bit macabre, obsessed with all things death to the point where he works with dead bodies for a living.