In my opinion it depends on every member not only dps and healer but it also depends if the dungeon is suitable for speed runs meaning there are no barriers (ex. city of amdapor,haukke manor hard) and hard-hitting moves like final sting. I simply can't remember which dungeons can be speedruned but the one that i cant forget is brayflox(hard) where, oh boy, it can be done with 3 pulls with not much effort.