@llaminm: Unfortunately, I have not used or come across Knewton GMAT Prep Course so I don't have any useful comments. I would say that most prep courses should be good to get you an above 600 score. But if you want to score above 700 then you need to find what works best for you. As you can see from debrief, it is a combination of things really. So if I were you, I would seek out some of the books/docs mentioned here and see if you find them useful.
The GMAT test is very good at finding YOUR score... what I mean is that you will normally hit the score that reflects your level assuming you don't have any other factors affecting you massively at the time of your test (nerves, migraine, etc!). So you can't really improve overnight... there are two ways to improve your score:
1. Practice (best technique and always helps). What I mean by this is not just going through
OG but say taking mock tests (10+) under exam conditions.. this sort of practice is very useful....
2. Finding a resource (book/docs/debrief) that gives you additional techniques that you were not aware of. In my case, I would say the Manhattan SC book and PowerScore CR bible made a big difference.
Also, a balanced score on Quant and Verbal will give you a higher overall score.. so a [Q45, V42] will be equal if not higher than [Q51, V35].... what I am trying to say is that if you have hit your plateau, say you repeatedly average Q45 in your tests on the Quant but you find some of these additional resources that can help you improve your Verbal from V32 to V36 then is makes more sense to shift your focus....