I can't remember any Roman document that identifies Christians as "pagans". I once heard that some scholars have suggested that one individual who was put to death on a charge of "atheism" was in fact a Christian, but I don't know how strong their case is. The Roman-era sources I have seen that take a negative view of Christians seem to view them as subversives.

I agree, though, that any use of the word "pagan" must be carefully examined in its setting. For example, if a modern-day ritual society preferentially calls itself "pagan" then it is making an implicit philosophical statement, and may be making an implicit historical claim as well. But if the group calls itself "pagan" only as a concession to the convenience of outsiders, preferring to refer to themselves as "The Society of the Mysteries of the Great Rattlesnake" or some such, then the situation is subtly different, and any claims that might be implicit of the word "pagan" as a self-designation disappear, though similar claims might be found to be made by other means.

T.