I would suggest going for the 5 books. The advanced quant really is more about strategy and tactics, but if you want to be sure you know all the basic and advanced content needed to get the most out of Advanced Quant, I'd personally go for all of the books. Also, that depends on which areas you make the most mistakes in and how much time you have until your GMAT. The way I see it, you are going to spend a LOT of money during the process anyways, so the books will just be a small fraction of your total expenses, anyway. Personally I score between 45-49 in the prep tests in Q (had 46 on real GMAT last year) and I have a lot of problems with the questions in MGMAT Advanced Quant
(and I am pretty confident within the basic material).