Hi Thomas,
did you already give a look to the release notes of the last 5.3.0.CR1 ?
http://docs.jboss.org/drools/release/5.3.0.CR1/droolsjbpm-introduction-do...
I personally worked to some optimization of both the MVEL library and Drools
internals and, as you can read there, this last release should should be
(accordingly to my benchmarks) about 3 times faster in both the supported
dialects.
Would be great if you could give it a try and confirm that you experience a
similar improvement.
Thanks,
Mario