I ran some benchmark tests to see what the Jaxen 1.0-FCS to 1.1-beta7 upgrade actually did for various PMD rule times. Here are the before and after numbers.

A couple of notable improvements - EqualsNull went from 5.2 to 3.9 seconds, OptimizableToArrayCall got nearly a second faster, and BooleanInstantiation dropped from 5.0 to 4.2 seconds. So, good speedups all around!

The benchmark class is in the PMD CVS repository, here's the code.