http://thementalist.wikia.com/wiki/File:Vlcsnap-2012-10-09-23h24m43s165.png
Looks like Brett Partridge in Pj's mind 

Red john is just under 6'0 thats a very precise detail. Plotnick is the only one 5'11

Finally, at the end of Black Cherry this is when Pj may have thought Brett partridge is Red John by the expression he makes. 
He looks at the page with partridge's name on it but he has it shadowed  with his finger symbolizing something, then goes to flip to the next page, THEN he goes to flip back again http://images1.cliqueclack.com/p/wp-content/blogs.dir/8/files/2012/11/mentalist-jane-notebook.jpg
 because the light bulb came on his mind! Watch the expression! :) Its partridge and it says, "Totally Macabre" common you know its him!

http://www.youtube.com/watch?v=7rjXOkCxUUw sarcastic voice around pj
http://www.youtube.com/watch?v=XGbq8LuACeg real voice