Why *p-*f?

[Peter &/or Graham]

>St. Augustine, who was well trained
>in Greek ...

St Augustine knew no Greek.

> St Jerome must issue forth the
>official Latin Vulgate "in good language."

The Latin of the vulgate is clearly very late Latin, not "good latin" in
your sense.   For example it includes phrases such as "dixit quoniam" (= he
said that ...).   In "good Latin" quoniam means because.

Peter