Well both the OPC and PCA share the same commitment to Scripture and conservative doctrinal tenets, including creeds such as the Westminster Confession...I know that PCA is larger though in numbers and is more “mainstream” —meaning we encourage crossing denominational “barriers” and actively engage with the greater Evangelical world. I think we also put more emphasis on evangelism and missionary work than OPC does.
Thanks. There’s an Orthodox congregation not too far from us and we’re planning to check it out. We’re ex-UCC (long ago) and Lutheran.