Even though there are only a few changes to the 5th edition, I would recommend getting it. It is too confusing to use an older edition especially if you are pressed for time or have never used this type of manual before.
Also I recommend marking your book with tabs such as in the "Reference Citations in Text" section or the "Reference List" chapter. Marking the book with tabs helped me find my way to the information that I needed over and over again. I've tended to use the same type of references throughout my graduate courses. You are a student or professional of the Social Sciences; you must write research papers. You are required to follow APA style and format for your writings. Action: You acquire the APA "bible," its Publication Manual, 4h edition. Problem: You now search for answers to your APA style and format questions. You scavenge for hours. Action: You know that the information you need is all there, but where? You experience the Psychological Rite of Passage known as the "Twilight Zone of Altered States of Reference Logic." Problem: The Manual is not intuitive. Solution: Develop your own cognitive cues and frames to make sense of the book's layout. Even though I was familiar with its third edition, I still used lots of post-it stick-em things temporarliy attached to sections. And then get on with it.

