It depends on the both the dungeon and the dps. With the SB dungeons and the general dumps to a good portion of AoE skills, I've noticed more and more that single pull runs and speed pull runs seem to take almost the exact same time since healers get far more time to dps in the single pull runs. Then again, it could just be the groups I wind up in....

As a tank in DF though, usually I pull two packs just to keep dps players quiet. Occasionally, I do like to just single pull just to see one of those idiots pull something else only to get trashed. Patience is a virtue, but in FFXIV, it can be a handy source of amusement at some antsy moron's expense.