...And with a few people yarding on a 9:1 your going to break the rope.
Anecdote for those interested - I was talking with a hydrologist acquaintance who works in a lab where they just tested various ropes under a 9:1 z drag and the results were...not good for the ropes. They had a rope snap back and break an aluminum support beam in the test tank where they were operating.
I speculating here, but I assume that they were using all sorts of rope, including some quality static ropes as their research is targeted to emergency professionals.
anecdote =/= data; But I wouldn't want to be yarding on a 9:1. If you do, check your vectors carefully.