When I'm tanking I always ask the healer how many mobs/groups they feel confident with me tanking at any one time. If they're new or if they are not overgeared for the dungeon, I always take it easy with the mobs.

I also look at the overall party composition. If the healer says "pull 4 groups" and I'm with a Summoner and a Monk I'll know that overall AoE damage will be low so I'll probably pull 3 groups.

When I'm a bard I don't mind speedrunning a dungeon as such because they are quite well-equipped to do AoE damage (the occasional free proc + Foe Requiem if paired with a caster). But when I'm a Monk I'm not very good at speedrunning because their AoE is poor. Arm of the Destroyer does pitiful damage for it's high TP (I only ever use it for its Silence effect) so I only use Rockbreaker for AoE every three turns.