Yeah, there are six nails I believe in Ifrit HM. In the lower-level dungeons it really shouldn't matter a whole lot as to who LBs. But, as others have stated, a melee DPS using a LB on a single boss is preferred, especially at higher levels. I like BLM/ARC for Haukke Manor, where you can group the three adds with the boss, and use the AOE LB.