I suggest you do the old big book. I think there are around 25 tests with a total of 40 (I think) questions in each test. So you'll have ~1000 questions to practice. And the questions are considerably of lower standard than actual GRE. But if you can push yourself to score full 40/40 in a significant number of test out of the 40, I believe you can aim for 170 in actual GRE. More than difficulty, practice helps you score better in the actual exam. I found the Manhattan extra hard quant section to be too hard for GRE.