I am more aligned with the OPC in many ways now. The BPC has a shared history with the OPC. When Machen and all the other conservative guys got the boot from the PCUSA's liberal majority back in the 1930s, that new denomination split shortly afterward with one group becoming the BPC and the other the OPC.
The BPC exit was led mainly by a minister named Carl McEntire. The BPC at that time was strongly Historical Premil in their eschatology and they didn't believe in drinking any alcohol at all. They have since moderated on both issues, allowing ordination of ministers and elders who are Amil or Postmil, and drinking of alcohol in moderation. But they have had several splits of their own since the 1930s, so the denomination is now pretty small. Only about 30 churches and 3500-4000 total members now, would be my estimate.