All right Vix, let me chime in & give you my 2 cents/paisa on your situation!
A very basic appraoch first- please work on your week points. As you mentioned that you are looking to overcome CR, RC more than SC's. My personal experience has been that
more often I could not get the right option or eliminate a seemingly irrelevant option just because I could not make out what the option means (read- lack of vocabulary & habit of not reading dense materials). Ask yourself how good you are at reading & comprehending lets say editorials (it's not that it will help you directly, but habit of reading editorials helped me immensely on RC, & to some extent on CR- for my preps I used The Hindu's!). On CR- there are many kind of questions.. identify your weak one's again- off late I see lot of questions on Assumption, Strengthen/Weaken, Main point, Evaluating Arguments (in the order of the frequency they appear on exam). I must also confess that when you reach @40 in the verbal section, it is the CR, which becomes quite deadly compared to RC's, SC's.
So what I would do if I were in your situation-
* Identify not only your weak areas but also the areas where ROI is best!. Please learn to ignore some arcane stuffs such as- I did ignore evil CR's, which were in range of V40+, complex P&C problems.
* More often I see folks spending sleepless nights over not able to break the hard questions and spending quite inordinate # hours on extra hard questions. Consider a situation- you are consistently scoring in the range 700 (+/- 20 points), still you are charmed enough to try extra hard & some super duper advanced one's. I mean what's the point? Ask yourself if you are scoring in the range of 700 or lets say 650, how on earth do you expect the test to throw a 750+ Q at you ? so to sum up know your ability and master those range of questions first, then move up step by step.
* Since you have not mentioned categorically what's the main problem in CR- is it simply you are not able to follow the logic, meaning problem? I would wait for your clarification on this...
* For RC- as I mentioned earlier in my experience the one's vocabulary & reading habit is a big determinant. So again I'll hold myself before giving any opinion unless you be specific about what’s the issue in your case.
Also one more thing about enrolling in a course just because it has a guarantee money back policy- I am sorry to say but I would like to differ with BB here. Course is not going to be different if you only take the part where you need help. I did the same mistake for signing up on Gmat pill for whole course, where as I needed more help on SC, RC only- on which it did help. Actually RC's method clicked for me, I would say. So do a cost benefit analysis for yourself & decide accordingly.
if you have specific questions, please shoot them up...
P.P.S.- all the points mentioned above are just my views & based on little experience I have had during my prep. your case/situation may be different, so it all may/may not work for you or anybody else.