I somehow pressed thanx by mistake!! :p

Anyways, OG is a representation of the GMAT. It gives you the patterns that the test tests. I personally believe that at the higher levels (720+) you will get harder questions than the OG. But they will test the same content in a twisted way.

The best way to see what the real GMAT holds is the GMATprep test. This will tell you how difficult it can get and help you compare the OG. This is more so true with quant, as some GMATprep questions are top notch.

Your percentage is good on the OG. I myself clock more than 90% (94/95%) on RC and CR and in the practice tests I usually get 1 CR and 1/2 RC incorrect. So if you want to compare you can. I am not as good on SC though.

Having said that use the OG to learn, keep going back to mistakes (even thought they are very few). Don't use it to gauge your level. Use the GMATpreps to do so!!

I hope it helps!

Great explanation, Akhil!

And this is all my own (hopefully educated) inference and nothing that GMAC has said officially, but it makes sense that the OG would be at more of the "average/above-average" difficulty level and not approaching the "the hardest question in this book is as hard as they'll ever get" level. The GMAT has a responsibility to make sure that you know what to expect in terms of content coverage and question format but I'd argue that it has a disincentive to giving away too much of the high-end difficulty. The test needs some unique-looking (but still based on the content and format of what you've already seen) problems to differentiate between the 680-720-750 students. So it only makes sense that the OG would hold those back...the GMAT doesn't want the test to be a test of "how well you studied" but instead a test of "how well you logically/efficiently solve unique problems".

So if you're looking for a high-600s to 700s score, I'd never look at the Official Guide as a perfect blueprint for the test, or measure yourself directly against the OG as a predictor of how well you'll do. What I'd do to supplement that is:

-like Akhil said, take practice tests in which they really have to throw you questions around your own ability level
-when you see OG questions, think like the testmaker: How could they make that question harder? Which answers were the "trap" answers and what was the trap that the test was setting? How could the GMAT test this same concept in a less-clear way?
-for RC and CR, look at some LSAT questions, which tend to be a little harder (since the LSAT doesn't have a quant section)
-think in terms of "takeaways" - not just "the answer is B...I'm correct" but "the answer is B and that's a good reason why I should always keep in mind _______________". The questions won't be the same necessarily on test day, but the takeaways will be.