When looking at this thread, I added my background commentaries to the ZIBBC volume on Genesis. The ZIBBC volumes themselves added fine. The "New Testament Background commentary" IVP Bible Background commentaries took a very long time (~5 minutes) to get added. During that time Logos was using 100% of a CPU thread.
Attached is a log, and a short video (only covers 45s of the problem). You can see from both that there's a huge amount of what seems like unnecessary querying of catalog.db
Log: 1374.Logos.log
Video: http://1drv.ms/1LDncs8