The GMAT is a beast, but it can be tamed - don't let one lost battle defeat you. I think that you are on the right track with your study schedule. If I were you, I would eschew the CATs for a few weeks and diligently study the OG. Once you have gone through the OG from cover to cover, completed and reviewed every question, then take a CAT. If you can confidently and accurately answer 4 out of 5 questions in the OG, I bet you will be able to score mid 6's on a GMAT Prep test.
Here's how I set my study schedule and moved from a 540 on my first GMAT to a 720:
- I would do one set of questions from the OG every night. I would do quant in sets of 35-40 and verbal in sets of 40-45 in order to simulate the duration of the test. I would not time myself, so I would sometimes take more than 75 minutes to complete a set. After completing my set, I'd take a short break and then go back and do a detailed review of each question. The review is where you will really improve. Make sure you do more than just glance at the answers in the back. You must make certain that you understand how to solve a quant problem or how to reason to the correct answer in verbal. Contrary to what you may think, the verbal section is not subjective. There are a limited number of principles that the GMAT tests over and over again. If you do enough practice problems, you will be able to identify what concept the test is asking with each question and how to work your way to a definite answer. Nearly every question you get on the GMAT will be a reproduction of a question you have done in the OG, only it will be with different wording or numbers. The concepts will be the exact same as the concepts needed to solve OG problems.
Now I mentioned that I only did one set of problems a night. Usually, I only did one set because it would take me roughly 2 minutes per question to do the first set and as a rule of thumb, I spent twice as long reviewing questions as I did solving them the first time around. So, to complete a set of 40 questions and then review the set, I spent about 240 minutes (40*2 + 40*4 = 80+160 = 240) or somewhere around 4 hours a night. Perhaps you will be able to pick up on GMAT wording and concepts quicker than I was able to, but in all likelihood, you need to brace yourself for an arduous battle. Uncommon results require uncommon efforts. Now get out there and slay that beast.
My GMAT Debrief: http://gmatclub.com/forum/my-gmat-experience-540-to-92850.html
Every man I meet is my superior in some way. In that, I learn of him. - Emerson