Difficulty level of Official guide vs GMATPrep

Dear Friends,

I have recently spoken to several people who took gmat and almost everyone said that Quant questions are tougher than the official guide questions or the questions they practiced. I would like to know your thoughts on below:

1) Are questions in official guides sufficient to reach Q50/51.
2) Are GMATprep EP1, EP2 mock tests higher on the difficulty side than official guides.
3) Are GMATPrep EP1, EP2 mocks similar in difficulty to official GMAT questions.

Thanks