pixel: It depends who the person is, if it is an outsider or someone who is in (like your wife). In your situation, i would *not* prepare a five minute talk and most *definetely* not with anything critical of the org. I think I would tell her about my doubts and ask her if this was something she felt you two could talk about and if so how. I would not tell her my full state of mind immediately.
Have you read books about cults and mind control? (for instance Steven Hassan?).
If you want to prepare to talk to her, a book i might recommend is actually "A manual for creating atheists". I don't know if you are christian or not and (despite the title of the book) I don't think it matters for this purpose. If you look beyond the "atheist street preacher" aspect (and idea which I think is pretty silly btw) I think it contains some good practical advice for talking with people about faith using the socratic method (which Steven Hassan also recommends) which is useful for undermining totalitarian faith-based views like the JWs.