GMAT Club tests

Generally I would suggest these tests to those who have mastered all the basics and exhausted all the official questions, those people who have reached 700 hundred level.
I would suggest taking GMAT Club tests way before your exam. As it will help identify your weaknesses in tough questions, you will have enough time to work on them.
Verbal: Very hard and may be discouraging, but will give a good indication of how you will perform towards the end of your actual exam.
Quant: Unnecessarily hard; some questions take more then 3 minutes, even those at the beginning of the test.
These were my experience, not necessarily have to be yours too.