%age accuracy

Yep, gabriel's right. You cannot gauge a score simply based on percentage correct, especially not from OG. You need to take a practice test.

You have two main options, each of which has strengths and weaknesses:

- GMATPrep, which will give you the most accurate indication of your current scoring level, but which will not provide you with any analysis or your performance or explanations for the problems you did

- a test from a test prep company, which won't be as accurate as GMATPrep but will give you analysis and explanations

So, you'll have to weigh the tradeoffs, obviously. If you are most concerned with the accuracy of the score, take GMATPrep. If you are most concerned with being able to use the test results to improve your score, take a test prep company test. If you do the latter, just make sure that the program actually will produce some kind of a report for you with analysis on timing and difficulty level in addition to percentage correct - otherwise, the data's not much use.