The short answer to this is there is no one answer.

Slightly longer answer: in practice I will usually do a few pulls in grit then judge how much stress I'm under to keep hate/be healed. If things seem to be fine I'll ask the healers if they are ok with stance dancing. If we aren't clearing or people need babysitting from the healers then I take the position that it's not my job to optimize my dps, it's my job to make things smooth. However, I don't live the pug life sooo.