Elektra would be a great opponent for Batman especially due to her training, her mental abilities, and her skills with with weaponry.
Blonde shadow's forum posts
Great theory G-Man in fact that theory was done in the first run of X-Factor after the events of Inferno when Madelyne Pryor died her memories entered Jean Grey and for some time cause Jean to have a split personality one was Jean and the other was Madelyne (Not to mention the Phoenix too but that is besides the point). This identity crisis with Jean and Madelyne was eventually solved once the Madelyne Pryor memories were sorted out in Jean's mind. The same can be done with Peter if he is going through the same experience as you said. He may need a telepath to intervene like Psylocke and her psychic knife.
I have to say Cap would win even though Batman has his gadgets and skill. The fact is Cap has the good sense to separate Batman from his utility belt and leave him with just his skill and the Bat suit. If Batman can get a superior footing on Cap then it will more than likely end in stalemate. I would like to put Batman against Phoenix powered Jean Grey now that would either be a short or extremely intense battle.
@Osian2: You forgot Scarlet Witch brought the people she killed back from the dead and she has been willing to accept any punishment anyone gives her. Wolverine has been willing to accept any punishment for the people he has killed. More important I'm an X-men fan every since I first saw them on T.V. I didn't even know about these Avengers until about 3-4 years ago, Being a fan of the X-Men and I know about the history of the Phoenix( even that fact the Jean Grey didn't receive the Phoenix force until after Madelyne Pryor died and that it was the Phoenix that killed itself on the blue area of the Moon not Jean). Surly common sense should have hit Cyclops in the first place to work with Captain America in the first place. Cyclops was right but so was Cap. Lets not also forget Hope couldn't handle the phoenix in the beginning when they were on the blue are of the moon she wasn't ready until she trained in Kun' Lun. Cable's training that finding the five lights didn't help her at all. She had to have the combined abilities of the Scarlet Witch and the Iron Fist the only powers that could counter or handle the Phoenix Force.
I'm just going to put this out there and shout it out mind you this is just a thought