I would randomly guess that if you were to take the test tomorrow .. you would get an even 600. The reason I am saying that is that GMATPrep is actually quite accurate .. and your scores do not fluctuate too much. However, your MGMAT and Kaplan scores are not too shabby either (and these tests generally are slightly more difficult). My wild guess is that you may have improved your test taking slightly as you moved from the GMAT Preps to the vendor designed tests.

Just keep practicing .. but don't overdo it as the last few days are crucial for keeping a cool head. I would suggest 2-3 more CATs (with AWA) to get you all pumped up and ready.

Oh ... and realize that I'm mostly guessing here ... its very difficult to just look at scores and come up with a reasonable theory

Good luck to you sir

My opinion......
Few months back I was scoring in the range 600-620....in GMATPrep and I ended up scoring 590 in the actual one.

After few months of continuous practise now I am scoring somewhere between 650-710, thereafter I rescheduled my exam which is on 20th Dec, few days after your date. So I do believe GMATPrep and I don't think the variation would be too much. Again if you can confirm from some more guys who appeared in the real GMAT then you can decide whether to take the test as scheduled or postpone it.

Got a 770 on practice, a 770 on a practice a month later, and a 770 on the actual GMAT a week later. My breakdown was different every time, but the score was the same. I personally had no standard deviation whatsoever, but that's just my case.