I have published the full comparison of the 6th vs. 5th somewhere on GMAT Club (and cannot find it anymore) but there is a copy on Amazon, so here is the analysis and summary what and if you should buy the 6th edition:
~~~ Comparison of the 5th edition vs 6th edition. ~~~
I have gone through all of the books and here is how it looks:
Overall, all books have undergone some degree of updating; not just slapping a new cover as some providers do, so you will be better of buying the 6th if you are deciding. If you own the 5th edition already, I would recommend getting only the IR and RC books, however as they have undergone the most transformation. The rest is organized better (more logical); it will help those who are short on time; the pages now also have more graphs, charts, and cheat sheets at the end (a number of books added this feature including Geometry and CR).
IR - substantial changes and improvements - the book needed them, and is now split by question type and organized a lot better
Quant - mostly minor updates (less than 10% new content)
RC - Major update
SC - Restructure with the main difference is that the idiom section is cut down and rewrite of most chapters (more than 20% of content updated)
CR - Improvements in text-heavy areas that put people to sleep before. Cheat sheets added after each chapter. I do like pre-thinking, however, in CR, so I still feel that CR book can be improved.
More:
https://www.amazon.com/review/R2K9YEAONP ... hisHelpfulHi BB, I am planning to buy just 1 guide to get access to 6CATs . Which one would you suggest RC or IR so that may help me ? I already have 5th edition full set.