I saw many ppl posting their practise score such as Q40 V41. I have read the gmat office site that the calculation of score is only possible by using a computer program (Which is not disclosed to the public). Actually how do they get their scores?
GMATPrep is the closet one in term of actual GMAT simulation and the algorithm used to calculate the score. Regarding tests simulations provided by other vendors, we need do a comparative evaluation of the score obtained. Take any test and compare your score to that of others. Go to "I just beat the GMAT" and compare your score with that of others who have already beaten the GMAT. Check their final score. That will give you idea, how you are doing?
Here are my perception about few vendors:
5 tests in Kaplan CD: Anything above 600 is good. Verbal is too tough and doesn't exactly simulate GMAT style. Your final GMAT score could be something 60-80 plus your Kaplan score.
Princeton: Read it's easy, but the final score would be somewhere near to your Princeton score.
MGMAT: Quants too tough, but the best to practice for the real GMAT. Scores will be close to your final score, though sectional score might vary a lot.

















