Most people pass, and most use World and glance through a bit of another resource. The majority of folks who take the test are busy interns and really aren't going to devote a ton of time toward the test. So yes they are "enuff" for a lot of people. The question is really are they "enuff" for you? Are you an above or below average person, based on the prior steps? Did you need extra prep on the prior two tests? Were you scoring well on World, or were you scoring <50% even the second time through? If you are the typical SDN superstar, then those are plenty. If not, then consider adding a resource (lots of people like Crush and FA.
In my opinion the key to Step 3 is speed. The questions aren't that hard, but many are crazy long, longer than you see on World. So do questions in blocks on world, and give yourself less time than the norm, to get your speed up.
