I'd be interested in knowing the answer to this as well.

Wanna know too.
I think it's way easier than Kaplan's or Princeton's.

It's interesting & genuine question.

Sometimes we feel the questions easier on book and paper. But when we actually face simulated test environment, say GMAT Prep test s/w. we get to know the level of difficulty.
Yes, it's true that OG 11th edition has questions in ascending order of difficulty. Your overall score depends on performance of both sections verbal & quantitative. Hence its a lot complex to give the numbers & range that would resemble particular score level.

I was hoping for more of an estimate. Is there any one else who would like to answer this? thanks