Hmm, I think I plowed through 5,000 questions. But that was inefficient. You want to extract as much learning from each question you see.
Manhattan Prep GMAT books in quant are excellent for quant preparation. From there, I'd say to find all the GRE quant books, and do all of the questions (verbal not as important). Unfortunately, lots of people have picked up on the fact that GRE Q is easier than GMAT Q, so percentiles have drastically gone up, even within the last few years. Even a few a years ago, a Q164 could have given you a spot in a top MBA. Now most MBAs have scores around 168-170. I talk about MBAs here, because they are the ones focusing the most on the standard tests.
Conclusion: probably buy the Manhattan Prep exams.They are certainly very tough, but they will give you the correct flavor of the actual difficulty. Book questions are no longer representative of difficulty on said-exam.
