In 3 John 2 my NA (27th, 1993) notes an interesting conjecture at the start of the verse. Instead of the words PERI PANTWN (for which the ECM notes only the singular variation of PERI PANTA in 945) the conjectural reading PRO PANTWN is noted (attributed to Piscator [I presume Johannes Piscator (1546-1625), rather than an anonymous angler, or some other red herring]).
This was also proposed by J. Rendel Harris (without reference to Piscator) in 1898 in view of the frequency of PRO PANTWN in documentary letters among the papyri: 'The recurrence of the formula renders it almost certain that in 3 John 2 we should correct the expression ... so as to read PRO PANTWN' ('A Study of Letter-Writing', The Expositor Fifth Series, vol. 8 (1898), 161-180, at p. 167.
In 1967 R.W. Funk (without reference to either Piscator or Rendel Harris), in view of the evidently close connections between 3 John and the common hellenistic letter, made the same proposal: 'The preposition is uniformly PRO (PANTWN) in the papyri (so Exler), whereas in III John it is PERI. The fact that the idiom does not appear to admit of variation and that PERI in the sence "above all" is otherwise unattested (refs B-D #229.2) suggests that PERI is a false reading. It must have been introduced by copyists who were familiar with the Christian but not the pagan greeting.' ('The Form and Structure of II and III John' JBL 86 (1967), 424-430, at p. 425 note 7).
Now it turns out that there is at least one first century letter which uses the form PERI PANTWN (BGU 885), so the uniformity determining the logic behind Harris and Funk is at least somewhat qualified (and a search might reveal more examples, and it might be that there was a usage of PERI PANTWN which meant something like PRO PANTWN, although that has not been demonstrated and BGU 885 is fragmentary at some crucial points). Scholars such as Klauck (EKKNT 1992) and Lieu (The Second and Third Epistles of John, 1986, p. 44) both suggest that emendation is not necessary, and that PERI PANTWN should be taken with the verb, meaning something like 'in all respects' (as RSV: "I pray that all may go well with you", and BDAG, 797). Another possibility would be to take PERI in an unusual sense (AV: 'above all things'; presumably following the Geneva: 'I wish chiefly that ...').