Usually, if you're going to see one of the final performances (and you're going to the fourth performance from the end of the run), rush tends to be more unpredictable, since all the procrastinators come out of the woodwork. Plus, the student rush is based on availability and the house for Friday is nearly sold out.
I did not do the rush, but I asked the box office attendant yesterday about it. He said they never know how many tickets they will have. Yesterday they were 6 tickets and he said everyone who got them was in line before 6am.