There has always been a running joke in the Drupal community that Dries is secretly working on a Java port of Drupal, using an SVN repository. While it makes for a good occasional laugh, there is some truth to that.
Now, Drupal on Caucho has been benchmarked and found to be 3.5 to 4 X faster than Apache and PHP.
This shows that PHP implemented in Java is faster than Zend's engine as an interpreter. These results are without an op-code cache for PHP though, and that needs to be benchmarked for a more comprehensive comparison.