Starting with the Sunflow Rendering System, which heavily stresses the CPU, the performance between Ubuntu Linux and Windows Vista was quite close. Between the official Java and OpenJDK build on Ubuntu Linux the results were very close.
Both the official Java implementation and OpenJDK were dramatically faster at file encryption through the Bork File Encrypter on Linux. Java on Ubuntu was about 40% faster than when using Windows Vista Premium SP1. Between OpenJDK and Sun's Java on Ubuntu, the results were nearly identical.