Whether you like it or not, members of the PCUSA consider themselves, and are generally considered to be, Calvinists.
The PCUSA does not regard itself as a Calvinist denominiation. I was a member of the PCUSA. Very few of the Presbyterians in that denomination have even read Calvin. Sadly, by this recent vote permitting the ordination of practicing homosexuals, contrary to the will of vast numbers of members in the denomination, the PCUSA has further removed itself from much of Scripture and the theology Calvin articulated and taught.
Neither the PCA nor the OPC capitulates on the Gospel and its teachings concerning homosexuality. Such modernism was part of what caused the denomination to splinter in the first place.
But by the grace of God, the remnant survives, regardless of men's ignorance and schemes.
And by this act the membership rolls of the PCA and the OPC will undoubtedly grow.
Why would anyone read Calvin if the Scriptures are sufficient? Why would anyone need to?