I still wish and believe that only Walter has the potential to be RJ. Who else could be smart enough to be able to use people and to play in PJ's league? 
Also, I am not sure, if the clue in 6x01 is really the pigeons. Could also be a sign that the pigeons come to the feeding hand. Lisbon has surveillance over all suspects of PJ's list and no one is near Partridge. Could this be one clue? RJ is NOT a person from the list? 
I also watched the scene in the house where Lisbon finds Partridge again and again and the strangest thing I recognized is that Lisbon is looking behind and looks at the wash-basin which seems to be cleaned. What could that mean? PJ once says that Walter has a minor dirt phobia...