Hi towerSpider,
The OG Books are great sources for practice problems that once appeared on the Official GMAT. The order of the questions in each of the content sections is "generally" arranged in ascending order of difficulty, although you'll come across questions in the middle and latter portions of each section that are rather "easy."
There are a variety of differences between working out of a book and taking a CAT (or the Official GMAT), so the score results are NOT comparable:
1) The book does not adapt.
2) The book likely does not offer questions in the same ratio that the Official GMAT will.
3) The "mechanics" of working out of a book are different from the "mechanics" of working on a computer.
4) On Test Day, you have to go through an orientation program, an Essay, an IR section and a break before you even START the Quant section, so your energy levels will likely be different.
Taking a FULL-LENGTH practice CAT is really the only way to 'mirror' what you'll experience on Test Day. As such, you have to do everything within your power to make those experiences "test-like" and realistic. You'll spend the bulk of your time learning, doing practice problems, quizzes, review, etc.; plan to take a FULL CAT every 1-2 weeks.
GMAT assassins aren't born, they're made,
Rich
