Hi prada,
From your prior posts, I think that you're savvy enough to know that NO individual book can 'guarantee' you a GMAT Score of 800. Furthermore, the 800 score is so rare (only about 100 Test Takers hit that score each year) that NO combination of GMAT resources can guarantee you that score either. Thus, assuming that you would be 'ready' to score 800 at any point in your studies is somewhat naive. There are a variety of factors that will impact your performance on Test Day - and only a few of them are 'mental'/IQ-based (the rest are physiological and psychological in nature). Thus, if you're looking to significantly improve your score, you have to consider far more than the perceived difficulty of a set of practice questions that you're working through.
There's a big difference between performing well on a small set of practice questions out of a book (that are likely all geared around the same 'limited' subject matter) and performing well on a FULL-LENGTH CAT taken under test-like conditions. Many Test Takers become overly-interested in the 'implied level' of the questions that they're working on instead of something far more relevant - WHY they're getting questions wrong. CAT 'review' is an important part of the study process. Here's a simple example of a list of questions that you should look to answer after you take each CAT:
After reviewing each section of your CAT, how many questions did you get wrong....
1) Because of a silly/little mistake?
2) Because there was some math/verbal that you just could not remember how to do?
3) Because the question was too hard?
4) Because you were low on time and had to guess?
5) How many Verbal questions did you 'narrow down to 2 choices' but still get wrong?
Once you define the specific reason(s) why you're getting questions wrong, you can work to 'fix' those issues and improve. It's simply not enough to state "I'm having trouble with '650 level' questions... so where do I find more of those?" Thankfully, the GMAT is a predictable, standardized Test, so you CAN train to score at a higher level. If you haven't hit your goal yet, then you have to consider how you can adjust your study plan.
GMAT assassins aren't born, they're made,
Rich
