Is Gmatprep SC harder than OG? That document with gmatprep SC is pretty tough, I think at least.
If you are talking about GMAT Prep test, then the test is adaptive. So the toughness level varies depending on the level of the test taker.
GMAC claims that the questions in OG are arranged in increasing order of difficulty. But yes, the last few OG-12 questions are really difficult ( at least I found them so, specially DS and CR )
