This is what is mentioned in Kathys book 1.6 edition -
"other than the addition of the System.Console class and Navigable collections, the
Java 5 and Java 6 exams are identical in scope. We recommend that you take the Java 6 exam and not the Java 5 exam, but if you do decide to take the Java 5 exam, this book is still appropriate. The new exam's objectives touch on many of the more commonly used of Java's APIs. The key
word here is "touch." The exam's creators intended that passing the exam will demonstrate that the candidate understands the basics of APIs such as those for file I/O and regular expressions".
I have known few ppl who have prepared only for 1.5 and cleared 1.6...but if are aiming for a very high score, probably
you should not take a chance.