Java on Windows Vista was even worse off when gauging the Monte Carlo performance through Java SciMark. Ubuntu's JVM was 3 times faster than what we were testing on Windows Vista! Between OpenJDK and Sun Java on Ubuntu there was about a 10% difference.
Our last SciMark test was looking at the composite performance. To no surprise, the best performance was exhibited using Java on Ubuntu. The Java SciMark composite performance was virtually identical between Sun Java and OpenJDK, but there was over 200 Mflops, or over a 50% difference, that separated Windows Vista and Ubuntu 8.10.