Well, not particularly different. The International Standard Bible Encyclopedia says that "Iona" may just be a contraction for "Ioannes" -- like Jack and Johnathon or Bill and William (except that Iona and Ioannes seem to me even more linguistically similar in pronunciation than those examples). Do you have any resources on the subject which would suggest otherwise? Thanks.
While I agree with you that Chilton's identification of Babylon with Jerusalem holds good for the Johannine Apocalypse, its use in the Petrine epistle is far more likely to follow the traditional Jewish intertestamental association of the term with Rome.
Why? Or, let me instead put it this way -- independent of the argument from later tradition that Peter wrote this Epistle from Rome, what independent arguments would suggest to you that Peter's Epistle is using the term "Babylon" here in reference to Rome, as opposed to John's Apocalyptic use of "Babylon" to refer to Jerusalem?
Also, do you have any citations which you could offer in support of the claim that "Early Christians often used 'Babylon' as a metaphor for Rome"? I'll say in advance that it seems entirely plausible to me that they did, but I've often heard this claim and I just realized that I've never asked anyone to actually present any evidence in support thereof (if you'd like to cite some, I'll accept a few texts demonstrating inter-testamental Jewish usage of "Babylon" to refer to Rome -- but only with the advance reservation that Gentile Christians would not have the Jewish Nationalist rationale for such usage, so I'd prefer to see evidence more particular to Early Christians if possible).
Honest questions, not trying to be tendentious. best, OP