Hi nithinjohn,
The most realistic CATs available are the 6 from GMAC (the 2 free CATs, and each of the 2 that come with Exam Pack 1 and Exam Pack 2), but retaking a CAT that you've already taken is NOT a realistic way to assess your skills. Seeing even a few 'repeat' questions can 'throw off' the Algorithm and impact your pacing, energy levels, fatigue, etc. Thankfully, the CATs from Kaplan,
MGMAT and Veritas are all 'close enough' to the real thing that they will provide you with a relatively realistic score assessment (assuming that you use the CAT correctly).
It's important to remember that taking lots of CATs will NOT make you a better Test Taker. A CAT is really a 'measuring device' - when used correctly, it will give you a realistic score and help define your strengths and weaknesses, but it will NOT help you to fix any of those weaknesses. To raise your scores, you have to put in the necessary practice and repetitions. The CAT will show you whether your studies are helping you to improve or not. As such, you really shouldn't take more than 1 FULL CAT per week. Based on your Score Goal and Official Score, the bigger question is what Tactics are you going to focus on learning during this next phases of your studies (so that you can EARN that higher Score on Test Day)?
GMAT assassins aren't born, they're made,
Rich