Hi superphily,
While a quiz bank can certainly help you to get in some practice reps, if you're notably far from your Goal Score, then that type of study is usually NOT a 'fix' - instead, you have to adapt how you 'see' (and respond to) the Exam, by learning and practicing the proper Tactics. Depending on how quickly and easily you can hone those skills, a large quiz bank of practice questions might not be required.
Before I can offer you any advice for your studies, it would help if you could provide a bit more information on how you've been studying and your goals:
Studies:
1) How long have you studied? How many hours do you typically study each week?
2) What study materials have you used so far?
3) On what dates did you take EACH of your CATs/mocks and how did you score on EACH (including the Quant and Verbal Scaled Scores for EACH)?
Goals:
4) What is your overall goal score?
5) When are you planning to take the GMAT?
6) When are you planning to apply to Business School?
7) What Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich