At this stage you have taken six practice tests and you probably have a good idea about your weaknesses. To strengthen any specific areas I recommend that you buy the Official GRE Quantitative Reasoning Guide. This guide has a set of 75 practice questions segmented by the following categories: Arithmetic, Algebra, Geometry, and Data Analysis. You can choose to practice selectively on the topics that you find the most challenging or do them all, and subsequently review my video explanations as needed.
The GRE Quantitative Reasoning guide also has three sets of 25 practice questions. Each set is a mixture of content and question types and consists of Quantitative Comparison questions, Multiple-choice questions, Numeric Entry questions, and Data Interpretation set. I would recommend that students complete each of these three sets in a time of 40 minutes. I have made the time modification based on the computer-delivered GRE General Test where each Quantitative Reasoning section contains 20 questions and you will have 35 minutes to answer them. These practice sets are excellent and are a perfect way to simulate the element of time and pressure of a computer-based GRE test. You can also refer to my video explanations for additional help.