Salutations "teddito":
I felt that USMLE World was much harder than the USMLE exam itself. Many questions on the USMLE exam were "one liner" types where you just had to know the answer. Some of the questions were long but for the most part many of them were medium in length. Lots of them were very simple and most of them were of medium difficulty. USMLE World really helped in the sense that the explanations allowed you to fully understand the topic being asked. In my opinion if you can get good scores on USMLE World then you should do fine in the USMLE exam itself. Good luck. Ciao.
"To achieve success, you must first define success."