Hi jasonfodor,
You've asked a number of different questions, so I'm going to answer them in the order that you asked:
1) The Diagnostic Test in the OG is a nice source of practice questions, but does NOT 'match up' with what you'll see on Test Day. In broad terms, some of the differences are obvious: it's pencil-and-paper, the question types are 'grouped' together and the number of each type of question is NOT what you'll actually see on Test Day. Other differences are subtle: the ratio of certain types of questions is not a match, the 'progression' of the difficulty level is not a match, etc.
2) Yes, there is a way to logically and properly integrate the OG16 into a study plan (as opposed to just working through questions in order, or randomly). It depends on the OTHER resources that you're using though. For example, our Course points to specific questions in that book (by page number and question number) so that you can practice specific tactics or concepts.
3) There are LOTS of different resources that you can use to study for the GMAT. Most GMAT Companies offer some type of free materials (practice problems, Trial Accounts, videos, etc.) that you can use to 'test out' a product before you buy it. We have a variety of those resources at out site (
www.empowergmat.com). I suggest that you take advantage of all of them then choose the one that best matches your personality, timeline and budget.
4) Test Date availability varies depending on the time of year. At certain times of year, it's relatively easy to set an appointment for the exact day and time of your choosing; at other times of year, it's more difficult (and you might end up booking a Test Date that is NOT to your liking). To maximize your chances at getting the exact appointment that you want, it's best to schedule at least a month in advance. As we move into August and September, the available 'slots' are going to fill up quickly. Now that the wait time is only 16 days between GMATs, there's also the possibility that more Test Takers will more quickly schedule their next appointment if they're unhappy with their Official GMAT scores.
I'd like to know a bit more about your studies so far and your goals:
1) What is your goal score?
2) How long have you been studying?
3) How have you been scoring on your CATs (including the Quant and Verbal Scaled Scores)?
GMAT assassins aren't born, they're made,
Rich