It depends. The OG problems are accurate for people scoring below around 80th to 85th percentile in quant. Above that, and you'll need to practice with some other materials for the harder stuff. I'd recommend taking a practice test to see if that describes you.

Also, remember that the OG goes in approximate order of difficulty, so if you're even scoring, say, a 650, the first 2/3 of each section should be fairly easy.

Solve OG is one thing. Solve OG under time constraint is another thing, totally different. You will be amazed on how low your score can drop when time is against you. Also, go thru the last 20 questions and then re-do it two weeks later….The impression you get when re-doing for the second time is that you hv never seen those questions before. (well,… at least this is my impression…).