TOPIC: Questions about the Premium Exams

Hello,
I'm currently subscribed and going through the premium PrepCast exams and I have a couple of questions:

1. What is the difference between each exam (not including the ITTO one)? Are they successively more difficult?
2. I've seen reference in the forums to Exam 7 as though there is something special about that exam - is there?

I've completed 2 of the exams so far but I found out I need to travel for work between now and my exam so there is no way I will be able to go through all of the exams ... so I'm curious if there are certain exams that I should worry more about.

Thank you!