The changes to the Java language between versions 5 and 6 are relatively small - version 5 brought much more new things. So, if you mainly use Java 5 features and something new from Java 6, the result probably isn't really a mix, but normal Java 6 code, since most of Java 6 is like Java 5 anyway.
I would, however, if table sorting is provided, at all (I think it is not explicitly required, but it is a common user expectation that tables can be sorted by clicking on the header), suggest that this should be implemented with the new possibilities for table sorting Java 6 offers because it is much easier. For me, table sorting was the reason why I have switched from Java 5 to Java 6 for the
SCJD assignment I am working on. With earlier versions of Java, there might be doubts whether table sorting should be implemented because it is not explicitly required and may make the code more complicated - but with Java 6 table sorting requires so little code that I think it is worth implementing.