Hi JustinChampy21,
The most realistic CATs available are the 6 from GMAC - but 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 correctly take the CAT in a realistic fashion).
There are a variety of factors that can impact how you perform on a practice Exam, including the type of Exam, the time of day that you take it, how well-rested you are, the number of little mistakes (or lucky guesses) you make, etc. If you took these CATs in a way that matches up with what you will face when you take the Official GMAT, then the results show that you likely have the knowledge/ability to hit your Goal Score on Test Day. It's worth noting that to hit 550+ on Test Day, you do NOT need to correctly answer ANY questions that you think are too hard or too weird (so you can afford to 'dump' those questions), but you have to keep the little mistakes to a minimum (especially on the 'gettable' questions).
Since you're less than a week from taking your Official GMAT, you have to be careful about trying to do too much studying. In these last few days, you should limit your studies to general practice and light review (NO CATs and NO 'cramming') - you would be better served by getting some extra rest so that you can go into Test Day calm, clear-headed and ready to work.
GMAT assassins aren't born, they're made,
Rich