Hi gianlucabac,
Test Day is a rather specific 'event' - the details are specific and they matter, so you have to train as best as you can for all of them. The more realistic you can make your CATs, the more likely the score results are to be accurate. The more you deviate, the more "inflated" your practice scores can become. Test Day involves a variety of really specific steps and parameters (including steps before the Test even begins - such as leaving your home, traveling, etc.). Every factor matters, including the psychological ones. When you sit down on Test Day, you KNOW that you're going to be in the Computer Lab for about 4 hours - but if you're just taking individual sections (or taking a CAT without the Essay and IR sections), then you KNOW that you'll be done in 1-2 hours. The attitude and energy that you use during practice will NOT be a match for what you'll need on Test Day, so it's not a proper way to practice. As such, from now on, you should plan to take your CATs in a realistic fashion (take the FULL CAT - with the Essay and IR sections, take it away from your home, at the same time of day as when you'll take the Official GMAT, etc.).
That all having been said, Quant Scaled Scores in the low-Q40s mean that you likely know most of the 'math rules' well enough, but you're making some little mistakes and missing out on LOTS of 'strategy-based' points. Thus, while a certain amount of content review would likely be beneficial, your focus should be on patterns, Tactics and the little 'secrets' to the GMAT. Given your timeline and goals, I think that you would find the EMPOWERgmat Quant Score Booster to be quite helpful. Most of our clients complete that Study Plan in under a month, so it should fit your schedule nicely. We have a variety of free resources on our site (
www.empowergmat.com), so you can 'test out' the Course before setting up an account.
If you have any additional questions, then you can feel free to contact me directly.
GMAT assassins aren't born, they're made,
Rich