It's good to go thru multiple exams, but trust all of us, Kathy and Bert's book is more than enough to get the exam witjh 90% plus scoring. All of us have done it. There are bunch of mock exams that are available for free.
Easiest way to figure out, if you are ready or not is, to play the cow game in this web site and the day you score consistenyl 100%, you are all set to rock and roll!
I have few mock exam papers that are in the standards of original exam, which i use for my students in my organization. Drop me a note @ firstname.lastname@example.org
if you would like to see them.