Manhattan Practice tests vs GMAC vs Actual

You should have a lot more faith in GMATPrep scores than in company test scores. GMATPrep is the real thing, and company tests are not. You've only taken one GMATPrep, and it can be a bit difficult to gauge your level precisely from a single test, for two reasons:

• Luck can play a bit of a role on the test (because sometimes your guesses work out well, sometimes not). It's rare though that luck will cause you to score more than 30 points from your ability level.

• One other thing to bear in mind, when evaluating a GMATPrep score, is whether your score might be inflated because you had seen some of the questions in advance. That can sometimes be an issue for test takers who regularly read posts on GMAT forums.

If there's no reason to think your score was artificially inflated, then you've demonstrated you're capable of scoring a 720 on the real test, so a 680+ score would certainly seem to be possible. If your score might be substantially inflated, then it's harder to judge. You'd get a better idea of your current level if you took another GMATPrep test, but this close to test day, I wouldn't recommend doing that unless you really need more test-taking practice (pacing strategy practice, mainly). You don't want to burn yourself out before the test - it does sound like you have a realistic chance to hit your target as long as you can perform to your ability, and you'll be more likely to do that if you take it a bit easy over the next few days and go into the test well-rested and relaxed. Good luck!