Originally Posted by
Niwashi
While many players do want to get to 60 quickly for other reasons, it has nothing to do with the armoury bonus. The only requirement for getting the full armory bonus is to have another combat class higher than your current one. It makes no difference how much higher. So, basically you're guaranteed to have it always available on all but one of your combat classes, regardless of whether you level one up first and then the others, or level them all up together by alternating evenly among them.