Does the GMAT Prep CAT predicts how well I will do on the real GMAT?

Thanks.

Yes, about as well as the real test predicts how you'd do if you took the test again. That is to say - within about 30 points either way (eg, if you get a 650, you're most likely to score in the 620 to 680 range). The one big caveat: how nervous you get during the real test. You obviously know that GMATPrep is just practice, so if you're the type of person who gets very nervous during the real thing, that can negatively affect your score.