First thing's first, it absolutely broke my heart to see Patrick's teacup being broken and his couch being taken away!
That aside, I am almost certain that it's not Bertram. Too obvious with the context of this episode, and also, he just doesn't fit my personal profile of RJ (and the show's profile of RJ!).
I feel that if it's not Bertram, then it must be one of the 'dead' suspects. If so, was it really so far off for all the Partridge theorists, then? They suggested he 'wasn't really dead' whereas now I can totally believe that RJ could be (and likely is) one of the 'dead' suspects. Because if it's not, then it's Bertrum, no? I don't know. Judging by the comments thus far (and screencaps from the E08 preview), I'd say RJ is McAllister.
One last thought. We were under the impression (from interviews and advanced reviews of the episode) that something/someone from season 2 was going to be coming back/revisited. Was that Rebecca? I'm a little confused about this. Maybe someone can leave a comment with an explanation.
Thanks guys. Thank goodness we don't have to wait 2 weeks for the next episode. I'm SO NERVOUS for the reveal. I just don't want to be let down!