General GMAT Questions and Strategies | Worth it to upgrade from MGMAT 4th ed. to 6th?

After an unplanned GMAT hiatus, I am back to study for my test (now scheduled for May 2017). I was planning on using my MGMAT 4th edition books, but would be open to upgrading certain books, if necessary (they are pretty cheap used). I've heard the CR book has been overhauled since the 4th edition, but wasn't sure about the SC or RC. Fundamentally, the material tested is the same as it was 2 years ago (minus the inclusion of IR), correct?


Thanks in advance for the advice!

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