Hi Warren,
First of all, congratulations on deciding tu pursue the PMP. It's a great step forward in your career.
I passed the PMP exam a few weeks ago on the first try relying only on Prepcast.
However, I tried answering every single one of the 2000 questions in the simulator.
I started very incrementally, only 10 questions at a time, then eventually, 20, 30, 40, 50, and then 60. Always using the timed option, to practice answering questions under time pressure.
I never scored much higher than 80% on my best attempts, and most times I ranged between 70-80%.
The questions on the Prepcast are rather similar than what you find on the exam. However, you do not see so many questions about the explicit Process & Process group names.
Although pretty similar, the user interface has some slight differences:
1. You cannot zoom in on the questions. The font is rather small on the screen, and I had a hard time reading the questions properly. I asked for assistance to the attendant during one of the breaks, but he told me there was nothing he could do about it. My workaround was to physically move the screen closer to my face so I can read more easily.
2. The strikethrough option (to rule out one of the answer choices) is significantly different, and in a bad way. On the prepcast, you can simply right click out on the answer and it will strikethrough the whole thing. On the exam, you have to manually highlight the question with your mouse and select the strikethrough option at the top of the screen to do the same thing. Not a big deal, some might say, but with 180 timed questions to answer, every little detail counts, and as I mentioned above, the font is very small and cannot be enlarged.
Best of luck for this!