GMAT Strategy

I'm about to take my 'diagnostic test' today and I have a couple questions:

1. Which exam should I take? I'm thinking about taking the Manhattan GMAT exam (out of the 6).

2. I've noticed quite a few posts about students getting 700+'s on their MGMAT exams and GMAT prep exams, yet they are scoring either in the 500's or the 600's. Can someone list out in terms of accuracy, the institutions that have the most accurate exams? Is it GMAT Prep, followed by MGMAT, followed by Kaplan, followed by blah?

Please advise!

It goes both ways. I've seen plenty of people report that they did better on the real thing than the MGMAT CATs. There are so many factors to account for in score fluctuation (ie an individual's ability to perform with anxiety, ability to adapt to different styles of writing and still apply the same principles etc...).

I think officially, they said there's like a 50 point margin of error, so if you're scoring 680, you could fall anywhere between 630-730, depending on how well you perform under the gun.

I haven't taken the actual exam yet - schedule to in a few days - but compared to the GMATPrep, I'd say the MGMAT is much more relentless on quant. Their quant is one tough question after another after another. The GMATPrep questions seem less intensive. That said, the practice scores seem to adjust to this. I would get about 16-18 incorrect answers in MGMAT Quant and score in the mid to 40's. I would get only about 11-14 incorrect in the GMATPrep but get around the same score (mid 40's).

Thank you, but a 50 point margin is huge!

Any other people help answer this?

Can I buy more GMATprep exams? (compared to the standard 2 that is gIven to people?)

As far as i know, you can't buy more.