I have not yet taken the PCAT, but I'm taking it in 4 days.
My overall impression is that memorizing Chemistry or Math formulas alone will not do anything for you. You have to truly understand the formulas and the various relationships that the variables involved in the equations hold to each other. Practicing Chemistry and Math problems is a MUST.
As for study materials, Dr. Collins seems to be very effective in Chemistry. I wasn't even a good Chemistry student in college and the Pearson tests place me at 80-99th percentile consistently, after reviewing it. I have never even taken OChem II, either. Dr. Collins Bio is good, but Kaplan's is even better if you have the time to study all the information it has.
Kaplan is great with Biology and General Chemistry, but is severely lacking in Organic Chemistry preparation. I hear Dr. Collins lacks in OChem preparation as well, but it seemed to have worked just fine for me, having never taken OChem II and scoring a B+ in OChem I.
As for Reading Comprehension, I think both Kaplan and Dr. Collins are insufficient. Kaplan doesn't even have any passages for you to practice on (at least mine doesn't), and Dr. Collins is too easy. I've never looked at PCAT Destroyer, so I can't critique that. However, I've been studying a book that was actually meant to prepare for the MCAT Verbal Reasoning section, and it seems to be very good practice. It is called "ExamKrackers 101 Verbal Passages in MCAT Verbal Reasoning". I would highly recommend having a look at it if you are struggling in Reading Comprehension, because the passages there are even more difficult than any PCAT Practice Test I've run into. If you can do good on the MCAT's Verbal Reasoning, I'm sure you'll also be fine with the PCAT.
For the Verbal section, I haven't studied this too much, but a lot of people seem to believe that Dr. Collins Verbal tests are pretty good. Kaplan is pretty weak here. Most people suggest that you brush up on your vocabulary, and I do too. Here is a good place to improve your vocabulary:
http://www.soundkeepers.com/GRE/
As for Quantitative, I find Dr. Collins a little too easy, though it's still worth a look. I hear Kaplan is insufficient as well. Pearson Practice Tests seem to be the most representative of the actual test in the Quantitative section, but I hear that's even more difficult than Pearson's tests.
So overall, I highly recommend Kaplan and Dr. Collins for studying Biology and Chemistry. Dr. Collins seems decent for Quant, but a little too easy. I recommend the EK book I mentioned above for Reading Comprehension, and for Verbal I highly recommend brushing up on your vocabulary as well as looking at Dr. Collins' to get a feel for the tests. I also highly recommend Pearson Practice Tests, though there's only three of them.
Looking at my post, it seems very choppy and disorganized, and I apologize for that. I pretty much just typed out my thoughts just as they came out.
