Hi jasonfodor,
Unfortunately, there's no practical way for the OG books (or ANY book, for that matter) to 'convert' a random group of questions into an approximate GMAT score. There are so many factors that go into Test Day that don't occur in a book (Computer-Adaptive Testing, random questions, 'ratio' of question types, time limitations, location, etc.), that the only reasonably realistic way to assess your skills is to take FULL LENGTH CATs under realistic and test-like conditions.
Since you've worked through a number of practice questions already, have you taken any CATs yet? If so, then what were your scores? If not, then you should plan to take one soon (perhaps this weekend) - you can download 2 for free from
www.mba.com. You should report back here when you have those scores and we can talk through the rest of your study plan.
GMAT assassins aren't born, they're made,
Rich