I think it's a bad idea to postpone just because of World. You will peak at a certain point, and you probably start to go down in your performance as you drag on the time before your exam just to finish World.
World is helpful, yes. It will allow you to see concepts in new ways. However, doing World two or even three times does not guarantee a great score. Use it for what it is: a tool to see different ways questions can be asked. However, that is only half the battle. Get your knowledge base strong via FA/Goljan if you want a decent score on Step 1.