Hi bcl,
The most realistic CATs available are the 6 from GMAC, but the 'accuracy' of a CAT score is also based on how realistically YOU go about making the CAT-taking process. For example, if you skip sections, retake a CAT that you've already taken, pause the Test, take it at home, take it at a different time of day as your Official GMAT, do anything else that is unrealistic, etc., then your score is likely to be less accurate (and in many cases, that ultimately means an unrealistic, artificially-'inflated' score result). As such, as you continue to study - and take practice CATs - you should put in the extra effort to make sure that each of those experiences is as similar to what you will face when you take the Official GMAT as possible.
Before I can offer you any additional advice for your studies, it would help if you could provide a bit more information on how you've been studying and your goals:
Studies:
1) How long have you studied? How many hours do you typically study each week?
2) What study materials have you used so far?
3) How have you scored on EACH of your CATs (including the Quant and Verbal Scaled Scores for EACH)?
Goals:
4) What is your goal score?
5) When are you planning to take the GMAT?
6) When are you planning to apply to Business School?
7) What Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich