I recently took and passed the 1.4 exam after several months preparation (thanks for the help, everybody). I primarily used the K&B book, and in the last month or so, I started doing Dan's mock exams(primarily Study Guide 1 questions). I would say that Dan's questions are considerably harder than the real exam questions, but that makes them very valuable for study purposes. The first time I worked some of Dan's questions, I felt a bit dumb, but they exercise you so much on so many details that when you get comfortable with them, you should have no problem passing the real test.
Also, working through Chisholm's questions from the Study Guides revealed what seems to me to be some holes in the K&B book. I studied Dan's answers and wrote little programs to work out my own confusions and get some experience in topics that I found I didn't understand. But it was his questions that revealed those misunderstandings. So, in short, his questions will seriously exercise you, and imho, if you can comfortably do them, you will be ready for the real thing.
Dan's questions are tougher than the ones in the actual exam. I suggest that you take Dan's mock exams after reading the K&B book. Then if you can go through Dan's questions you'll be very confident when you're taking the exam.