Thank you for your replies so far!
Veritasprep -
Yes, I have taken the IR and AWA for each of those, since I know it can make a huge difference. The time of the day was always exclusively mid-morning to noon, with the exception of the last CAT where I did not have enough time in the morning and had to finish the verbal in the evening, though I actually felt more focused when I did it then (the results obviously point to the opposite). I have generally reviewed my errors (with a few exceptions) for all tests and exercises I have done so far, but I never feel like it is very effective after CATs. It is difficult to remember when I review the day after a CAT, but when I review on the day of a CAT i have trouble concentrating. Would it be better to always review immediately after nonetheless? Another problem I found is that sometimes I simply don´t know how to categorize all errors, I often find that I look at Quant errors, see what I had done wrong and then go "There is no way I would have known how to do that" (Often because I never came across a similar problem in my preparation so far). For Verbal, 90% of my mistakes are stupid mistakes, so last CAT I actually gave myself more time per question (I tend to somewhat rush through Verbal) but that did not help.
Rich -
Yes, I made a typo there (it was quite late at night when I wrote the original post) and there was never a 550 CAT, it should say 660. I have been following EmpowerGMAT since July 10th, and originally completed the 3 day trial and got up to the first CAT (I wanted to see whether the tactics would get me anywhere, but I did not watch all explanation videos back then). I got up to the first CAT, then had to take a few days off due to personal reasons and then re-enrolled and finished the course up to the 2 CAT mark, this time watching every video. I saw improvement in my scores for quizzes and was quite pleased with my progress so far before I took the second CAT on the Empower schedule. I have not been able to follow a study plan completely, since my study schedule was a bit disrupted since I was not at home for the past 2 weeks, but I still made a point of completing a few modules per day. Since I followed the course, I most recently focused on CR and Algebra. I was originally hoping to refrain from taking the second official CAT before the end of my training, but I guess it makes more sense to purchase another CAT than to sacrifice my score.
On a sidenote, I always run out of time for my last 10 Quant questions, I have no idea how to improve this, since I originally thought it would fix itself over continued study and since I have no issues with timing on practice quizzes. When it comes to triage in CATS, I often have trouble finding a lot (or any) answers to triage, even though I have now reviewed (and completed) that module many times. Another sidenote, I have noticed when I looked back that my first three questions are always perfect and put me in the 99% percentile on both Verbal and Quant, but I always get the next few questions wrong.