http://www.developer.com/white_papers/article.php/391172/Java-SE-6-Performance-Improvements.htm
Many new features and enhancements in Java Platform, Standard Edition 6 (Java SE 6) are aimed at improving performance and scalability. Major areas of improvement include runtime performance, garbage collection, performance-related default settings in the 6.0 Java Virtual Machine, and client-side performance. Runtime performance improvements include: Garbage collection performance improvements include: Client-side performance improvements include: Benchmark tests showed marked improvements over Java SE 5.
Java SE 6 Performance Improvements
February 15, 2010