I recently passed this exam. I was not aiming for a perfect score but instead wanted to fast forward to what has happened to Java after version 6 (and wow I was amazed by it) - so my aim was to just learn as much as I can while my 2 year old is asleep during nights. :P
I would like to thank Bert and Kathy for keeping the OCP certification book very much alive and interesting to read (totally worth the hard copy I brought from amazon). The last I read was when it was still with Sun (version 6 of jdk). The book still has its spark and this was my primary reference to pass the exam. I did not take any exam simulator, neither did I finish the exams that came with the book (Nit: CD ROMS are so 2013 :P).
For the upgrade exam it was heavy on Streams / Lambdas and Modularity. It was also very current with using streams - especially with var types, and with recent enhancements after jdk8. The book strengthened my fundamentals about the topic except Modularity. Since I am a big red employee, I got hold of the jdk 11 modularity training that Oracle provides:
I highly recommend it to anyone (shameless plug) who wants to pursue the exam - it pretty much covers whatever gap is left between jdk 8 and 11... until B n K comes up with a more recent book ;)