Do fewer questions but really dig into those questions. And you don't need to limit yourself to one source - again, this is not about "finishing" a source. It's about fully learning what you need to learn for whatever question is sitting in front of you right now. Then, when you're done, move on to another. But don't set an artificial "oh, I need to do X questions" and then just plow through them without learning what you need to learn.
When you say you're using CAT questions, do you mean you're just using them for problem sets? Or do you mean you're taking a bunch of full CATs?
CAT exams are really good for (a) figuring out where you're scoring right now, (b) practicing stamina, and (c) analyzing your strengths and weaknesses. The actual act of just taking the exam is NOT so useful for improving. It's what you do with the test results / between tests that helps you to improve.
If you're just using the questions as problem sets, as you would the Advanced Quant questions, then that's fine. And either set is fine - they're similar. But if you're taking a bunch of CATs, stop - you're studying really inefficiently!
You should be doing this kind of analysis when reviewing practice problems:
http://www.manhattangmat.com/articles/a ... roblem.cfmThat kind of analysis takes significant time. I might take 5 minutes, or 10 - or sometimes 15! - to analyze a single problem. But that's where you're really learning.
Now, you don't need to answer every single question in that article on every single problem, nor do you need to write out a report on every problem. But you should have the list of questions in front of you and consider each - which ones do I really need to think about for this problem sitting in front of me right now? (And don't neglect the questions you get right - it's often easier to find timing shortcuts, spot traps, and learn how to make educated guesses when you got the problem right.)
So what I would really recommend is a mix of our questions and official questions. Our questions because our explanations are a lot better than the explanations for official questions - we help you learn more - but official questions too because there's nothing better than the real thing as far as the questions are concerned.
So do a mix - you don't have to focus on just one source. Our stuff, GMAT Focus and/or OG12 - it'll all help. :)