I'm currently on Book 6, but have been slowly trudging through them for the past couple months.
My strategy was/is:
1) Review Books 1-5, doing every problem at the end of chapter, but NOT doing any of the OG problem sets or Advanced sections. Taking detailed notes on each chapter by hand. (took about 4-5 weeks)
2) Summarize the "easy" sections, do the OG Quant
v2 problems, and then review the Advanced chapters, taking detailed notes, and finishing the Advanced OG Quant
problems. (took about 2 weeks)
3) Review Verbal books (6-8), taking down notes, doing the OG Verbal
problems. (in the middle of this right now)
4) Quick-review the Math section, do OG 12ed. problems.
5) Summarize the Verbal section, do OG 12ed. problems.
6) Run through a week or two of practice tests, and hone down sections I have issues on (SC, Word Translations, and general DS right now).
My diagnostic test had me doing well on Verbal (40) but slow on Math, so I tried to focus more on the Math books. I just took another diagnostic that had me great on Math (48) but my verbal skills decreased (36), so I'm thinking I should've balanced my studies more evenly.
I'm getting good results by the initial review + writing notes, then a re-review. The only problem is that it is slow. It first took about 2 hours per chapter, but I'm getting it down to about 1-1.5 hours. Cutting out the unnecessary examples and summarizing less on paper. The note-taking part is pretty important to me -- I'm sure I would've missed some key points if I just quick-skimmed through the chapters.
How much time are you spending per night on your studies? When are you looking to take the GMAT?
Discipline + Hard Work = Success! 770 (Q50, V46)