Good question. A general indicator would be to get at least 80% on all the exams, and I do recommend you take all of them. Please understand that everyone is different and that the actual test may be interpreted as easier or harder for some folks.
Focusing on just the simulator will go along way, but I would also recommend you you look around for some free questions, based on the new PMBOK, that would add to your training. Some questions have different wording and varying degrees of difficulty which should help you. Realise though that some free questions are so difficult that your scores may drop a lot, but do not let that worry you. Focus on how the questions are written and the context of them.
The actual PMI test is something I would not call straight forward, in that you really need to understand concepts and think out of the box with them. The cut and dry answers may not be there.
