You know what, I have no idea! I have a feeling that anyone else's comment would be pure speculation.
Here's what you should do. Punch out secondaries as fast as you can, but do the best job possible. Hahah, it is as you feared. You have to produce something as good as your personal statement in less time. Have fun!
My advisor warned my to be very careful in what I say in the secondaries. He said be sure that you can defend ever single topic and statement because many interview questions come from these essays. He suggests reading a copy of everything you send just prior to an interview and even taking a copy of all essays to the interview to be able to refer to them. He has said that the worst thing that you can do is make some statements about your research or clinical experiences and then be like "duh" when asked to expand on them in the interview.
I know University of Chicago does their initial screening just on the secondary. (The dean mentioned that at the interview) I think it varies from school to school. But the only school I remember asking me something about my secondary was Baylor.