practice questions from Official Guide adequate for prep?

I've been going through the questions offered in the Official Guide everyday.

I've been told that these question are representative of what will be on the actual GMAT. However, I've also had people tell me that are woefully inadequate if you're looking to score 700+. The questions on the Official Guide are dumbed down to represent the average GMAT crowd of those most likely to score around 500-600.

What I've noticed is that usually questions 1-60 are fairly ridiculously easy. The questions toward the end (questions 150-230 are more difficult).

For questions 1-60, I've been scoring about 95% of them right. Should I just be focusing on the harder questions (I know which were the harder ones based on what the Manhattan Official Guide companion tells me if they're either a 300-500 level question, 500-600 level, 600-700, 700-800 level, etc).

My assumption is that you want to consistently be able to answer the 600-700 level questions, and be answer maybe half (or more) of the 700-800 questions right if you want to get a 80%+ percentile quant score. If you're doing well on the test, you're going to get those "hard ass" problems, but if you get those wrong, then you'll get a 600-700 question, and if you get that right, you'll get another 700-800 level question etc.


I'd love to get people's take on this.