It really doesn't matter which editions you use.

With each edition, we try to perfect our explanations, add clarifications, fix typos, or rearrange the ordering. In the 6th edition, for example, we added explicit chapters on "working backwards" and "picking smart numbers," whereas before those strategies were just sprinkled in throughout. None of the content will have changed, though. The same applies to the OG.

You have plenty on material to study with!