You can usually find out the essentials of a revision or new edition by opening up the new book and looking in the front where the publisher will list what is new in this edition. As a rule of thumb, it does not matter for Excelsior if you have the latest edition. I have the 6th edition of Wong's and am doing quite nicely with the peds questions for Excelsior. I'm getting most of my studying done from NCLEX review books anyway. I only use the references to do added reading for understanding or to look specific things up, I'm not plowing through all those texts. But that's just me.