The MasterExam is - based on what I have heard - easier than the real exam.
If you score 78% on MasterExam you might - based on my personal guess (remember that I have never taken the exam, but some mock exams are much harder and after taking many mocks you get a sense for rating test difficulty) - expect to get between 60% and 70% on the real exam. While this is passing (better than 52%), it is pretty close to failing.
You want to be scoring around 85% on MasterExam (and similar mock exams) to be 100% sure that you will pass. Otherwise, there is a small (but not impossible) chance that you will FAIL.
Some companies may ask (one day) what your score was. So it may be better to get something like 80% on the real exam than 60%. This again is a matter of opinion. It all depends on your situation and the reasons you have for wanting to get certified in the first place.
Again. These are only my opinions.
You may want to talk to others to get their opinions.
Anybody have something to add to this topic? [ July 23, 2006: Message edited by: Douglas Chorpita ]