I think pull size is largely dependent on the skill level of your players and the ilevel of their gear. An undergeared tank or one who doesn't know what a cooldown is should not be making large pulls. Some healers can't handle the healing of a large pull regardless of tank skill/gear. Some dps can just wreck a group, others can't, and if the dps aren't up to the task of killing quickly there's no benefit to a large pull. Ultimately, there's no right or wrong answer here, it all comes down to who the roulette paired you with.