As GMATPrep was produced by the GMAC, *most* people find it more accurately reflects the real test and thus is most accurate to the real score.
Note: *most*, you never know what will happen on test day, so don't take it as the holy grail. Most people have reported MGMAT quant harder than the real thing.
Your quant is stable and you've seen a consistent increase in verbal. Those are very good indicators, more so since you have not repeated a test (i.e. resetting GMATPrep and seeing repeat questions).
We have an estimator tool:http://gmatclub.com/gmat-score-estimate/
With your remaining days:
Brush up on your weakness and shortcomings, get the last GMATPrep test in and MAKE SURE YOU RELAX THE DAY BEFORE. Do NOT burn out.
Also, take adequate supplies with you to the test center (banana/energy drink/power bar). Take full advantage of your breaks .
Best of luck,
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