Both 5 and 6 version of the book are mostly the same, but the 6 version covers some topics more than the 5 version and has more examples and stuff. So I recommend you to go for the 6.0 version if the book...
For either version 5 or 6 of the exam I would recommend the version 6 book. The newer book covers all the topics for both exams. It's VERY easy to know which topics (and there aren't very many) are for the version 6 exam - so even if you take the version 5 exam you can spot those few topics that you can skip. Finally, the new book fixed some errors and added a LOT of new mock questions.
Eliminate fossil fuel subsidies. (If you're not on the edge, you're taking up too much room.)