Pang,
First the standard disclaimer: Performance on the PrepCast Exam Simulator may not translate to performance on the exam.
There are plenty of posts on the forum that lead me to think that in order to be fully prepared for the exam, simulator scores should be in the 80%+ ranges. 60%-70% ranges indicate that you'll have a low probability of a pass on the PMP exam.
You should also prepare by taking full, 4-hour examinations. While the examinations draw from the pool questions, the full-exam will prepare you mentally for the stress that is induced by having a count-down clock displayed on the screen as well help build up mental stamina for the exam. Understand that a 4-hour, timed, professional examination is tiring both physically and mentally, and you will feel "drained" by the time it's over even in the best of settings.
Good luck.
Harry