[Kekephee]

Assuming you're not going to misstep and die (which Muteki already mentioned as a factor) a good rule is, go as high as you can go before you start getting a significant enough number of resists to make it not worth it. When I was in SK doing aviaks, sometimes I'd get avocets that were too high compared to the other mobs I was killing, and when the last of the other mobs dropped the avocets would be 50 or 60% hp. At that point you have the choice of either zoning the avocets or taking them with you to start your next pull and dropping them over the course of 2 or 3 pulls.