54 is correct. Some tips for Vanquishing: Bring an MM or 2, they make it so much easier and make sure you balance out healing and damage to something that works, I don't know how many times I've gotten down to the last couple groups only to die because we didn't have enough damage to take down a boss or something.
One thing to note, you don't have to have every mob in a zone dead, you simply have to have killed every mob. What I mean by this is in some zones in the game, you'll run into mobs that res their buddies (especially prevalent in NF and Factions), once you've killed a mob, even if it's then res'd, it counts as done so far as vanquishing goes.