Please, see this 33 page thread ( http://www.shsforums...?showtopic=3599 ) that argues back and forth, pro and contra, striving to answer these particular questions. It is a good if long read.
You are so mean. I decided to spare myself the 33 page discussion. I voted no to Irenicus raping Imoen.
In the game, we never really hear the pc's reaction to the torture. There are a several passing comments on the subject but the comments are shallow. Why not have Imoen and the pc have a discussion about their mutual experiences?
I don't think the general story needs anymore drama. The story has so much angst already, why add more? I think the rape aspect would tilt the story to parody.