Soccerfan, I can't tell you how relieved I am since reading your post and its subsequent replies. I scored around the 650 range with the Princeton and PowerPrep practice tests, and took my first Kaplan practice test last night. I received a 550. Granted, I didn't manage my time very well on the verbal section and, therefore, had to blindly guess toward the end, but I was deflated nonetheless by my final score.
I am going to stick to the Princeton/PowerPreps for truly adaptive CATs, and take CEO's advice and only use the Kaplans for timing.
This forum is such a great find.