I've taken two GMATPrep mock tests, and scored in the 95th and 99th percentile in the verbal side of the equation both times...
However My quant scores have been bad enough to bring me down to 690, and 670 respectively.
I'm a bloody investment banker, so this isn't beyond me... What is the best way to bump my score up most effectively over the next week before I write?
You can perform a 2 step action -
1. Make sure you are aware of all the involved concepts for each Quant topic. The best way to identify this is by analyzing your practice test results. Chalk out the topics where you score lesser and revisit the entire topic in detail. For example, for me 'inequalities' was a pain in the neck which I improved by a lot of practice.
2. Secondly, try to attempt more and more full time Quant tests. This will help you in increasing your speed which will eventually help you score better. Also, go through the questions after tests to learn and improvise upon the ones you got wrong.