First off - Paul himself claims to be speaking of another man.
Is he really?
I presume this is based on v5 yes?
However reading v5 in that way is a failure to follow Paul's argument - if he is speaking about anyone other then himself then his words are pointless - they detract from the flow of his argument rather then add to it.
So, why does he address his own experiences in the third person?
Well, maybe it is the rhetorical device of pseudonymity in apocalyptic writings - as a jew trained in the conservative school of Gamaliel that would have been part of his training.
The describe the event in the third person might derive from the very nature of the event itself - it was like he was watching himself experience it - consider what he says about not knowing if it was in the body or out of the body - v2.
Or maybe because of the way his opponents were boasting he decided to step away from such actions as he spoke about his own spiritual experiences. When we consider v1 we see Paul saying, 'it isn't helpful to boast, therefore I will talk about vision that I have had instead' (or at least that seems to be the best sense we can make of his words)
Second - I believe Paul.
On the surface that sounds very pious - but actually it isn't - it is careless!
You seem to be suggesting that those who disagree with you do not believe Paul.
Now, personally it is my opinion that the person who believes Paul would take the time to read what Paul has said and take the time to meaningfully interact with what others have said in relation to Paul.
Why is it, I wonder, that the Genevan school of thought that produced the bible translation you so highly esteem believed this was Paul speaking about himself?
As to who it was Paul was referencing - John the apostle is the only one ever spoken of in the NT as doing such.
Where does the NT speak of this happening to John?
I can only assume you are referring to John's experiences that he recounts in the book of Revelation, can you point me where he describes his experience as being the one Paul describes - there is no reference to 'the third heaven' in Revelation, and as far as I can see whilst John gets to look into heaven he always seem to be outside of heaven - looking in (Rev 19:11 etc) and he is hearing voices coming from heaven (Rev 10:4) - his experience is not the same as Paul describes.
So, it isn't John, and if Paul isn't speaking about himself he is wasting ink and taking away from the flow of his argument against the false apostles in the church at Corinth.