I tend to pace myself according to the group. If I have two runners I will just run with them. If I have two guys who are chilling and killing I will join in. If I have one of each, my tendency is to hang with the guy at the back and help him out - he may be new, or he might just like shooting stuff. I like shooting stuff too. In that situation the runner can solo the boss, sit and sulk, or just leave.