Unfortunately, it is very tough to "pump up" scores in a few days. For the most part, you should expect to score on the real test whatever you have been scoring in the week to 2 weeks before the test, ASSUMING you have taken the practice tests under official testing conditions. Do not assume that your score on the real test will be higher than your practice test scores. The few times that does happen for someone, we call that "lucky!" :)
Official testing conditions include the essays, two 8-minute breaks, taking the test all in one sitting, not eating or drinking except on the breaks, etc. If you have not been taking the tests under official testing conditions, then your test scores may be artificially inflated. (For instance, skipping the essays leads to an inflated multiple choice score for a lot of people - not everyone, but many.)
You do not say when you took the other tests. GMATPrep is the closest to the real thing, so those are the scores you should pay most attention to. Your two GMATPrep scores are 650 and 680 (the latter score also represents your highest test score). Assuming you took those under official conditions and assuming you took them fairly recently, you should expect something in that neighborhood on the real test.
BUT you should also try to figure out why your score dropped so much on the Princeton Review test so that you can avoid having that happen again. This article can help you figure out what might have gone wrong:
http://www.beatthegmat.com/a/2009/10/26 ... went-wrongSo, now what?
If you absolutely want a 700+, you should consider postponing your test. If you will be okay with a lower score, then you may want to go ahead and take the test, but only if you can figure out WHY your score dropped on this last test and what you can do to prevent it from happening again. (You won't figure that out by taking another practice test, by the way. You may figure that out by doing the analysis described in the above article.)
I absolutely forbid my students from taking a practice test within 3 days of the real test, ESPECIALLY if the student's confidence is low. There is really no great upside to taking a test that close to the real thing. In the best case scenario, you do really well and your confidence spikes, BUT you tire yourself out right before the test - which possibly causes your performance to drop on the real test. Alternatively, you don't do really well, your confidence is shot, and you have no time to do anything about it before the real test.
It really comes down to this: what's your drop-dead minimum score goal? If it's higher than your practice tests, postpone your test.