Startup addict, I do disagree with you on Gmatprep containing 10,000 questions. Even so, if you are performing at a high level you will see the same questions regardless. Also, just because the questions are numbered in the 10,000 range, does not mean they are in order, and every ID is a question.
However I do agree with you that doing as many gmatprep exams does help, however I do not feel it will be a reliable indicator of your score after 2 or 3 attempts. I took my 5th attempt yesterday and score a 48 V ! However I do distncintly remember 3 or 4 questions that I probably would have struggled with, but were familiar to me in that I knew the answer, or at least the direction I need to go in. Then again I scored a 44 on math, whereas my previous tests were all in the 46-50 range so I guess I can't go both ways with it.
Also, I believed when people said all questions count equally, but now I do not. The gmatprep I took before this, I got the first 3 questions wrong, and then the next 34/38 questions right and landed a 37. Yet other times I have gotten 6-7 wrong I scored 42-44. I'll never understand. I just know I WILL pay attention more to the first set of questions, and if I know I was iffy about a question previous, I will spend extra time on the following because consecutive incorrects seems to hurt a lot.