first, where in AZ?, i live in Tucson.
second, the big difference between the PCA and the OPC is what i call center of mass and width of acceptable positions..
most organization have a crucial list of must believe principles. The PCA and OPC have such a list, but more for Teaching Elders then for anyone else.
you can try to map a right left axis on most of these principles. for example:
on the issue of women in the church:
rightmost, no women speak in public at the church. just to the left is women speak only to groups of women. a little bit more to the left is women speak to groups of men and women but don't teach. then women acceptable as Sunday School teachers, then as deacons, then as ruling elders, then as teaching elders, then the position that women must represent on a session the same % as they are in the church.
almost all issues can be plotted this way. it shows a variation in potential beliefs. well, there is an acceptable right and left point in most groups. for instance, in both the PCA and OPC there is no one pushing for the ordination of women as teaching elders. there may be a few women deacons but probably are no ruling elders, where the EPC has a few women RE's.
what is interesting, at least to me, is to map out what looks like a cap over the organization which is the length between the rightmost acceptable position and the leftmost. the OPC seems to have a shorter acceptable distance, that is they are more homogeneous on most issues than is the PCA.
another issue i have thought about is this center of mass idea. Where do the majority of people in either church fall in this continuum of beliefs?
the PCA appears to have a center of mass a little bit to the left from the OPC on nearly every issue i have studied. Not just a wider acceptable viewpoint, but the majority of people in the OPC are to the right of the majority of the PCA.
another issue i think is important, is the relative theological sophistication of the two groups. the OPC consistently strikes me as having a more educated laity then the PCA.
that being said. i am comfortable with and have been a member of both churches, as well as the EPC.