I'm studying for the 1.4 exam and have been taking mock exams from 2 sites mainly. These are Dan Chisholms & Marcus Greens. Both are excellent resources (pay the money at Marcus's!).
There does seem to be quite a big difference in the difficulty level between the mock exams however, with Dans being much harder. I can score over 80% on Marcus's exams but Dans are coming in around the 50-60% mark.
On the mock exams list on JavaRanch, Marcus's exams are said to reflect the difficulty level of the real thing very accurately. Therefore should I be that concerned that I'm finding Dans exams harder?
Dan himself said that he intended his exams to be used while learning the objectives but not as a simulated SCJP examination. So expect to score lower, especially if you are not learning Java from a more thorough textbook.