For what it's worth I've been testing it this season again.
Thus far we've got 745 innings caught for
Miguel James (68 PC). He naturally got tired so we've given 377 innings behind the plate to
Martin Berry (a SS with 19 PC) because by this point I've become convinced that PC is meaningless.
On the season, James has a CERA of 3.064, Berry has a CERA of 3.032.
Realistically the biggest difference is that James throws out only 15% of runners, whereas Berry throws out 31%. For what it's worth Berry also has a lower passed ball rate. At this point I think I may choose to start James for his bat, but bring Berry in as a defensive sub late in games. He looks to be the better defensive catcher (or at least James' equal) and this will keep James fresh otherwise.