Busy load testing an application that makes use of jboss messaging. When performing load testing, it seems that messaging seems to be the bottleneck in performance.

Using 2 queues, configured to be clustered, and messages are non-persistent. the persistence service is mysql (DefaulDS = mysql over network).

What parameters would help improve performance?

My assumptions would be:
change persistence-service to local hsql.
DefaultRedeliveryDelay - change from 0 to 1. is 0 immediate? 1 = seconds or ms?
Would MessageCounterSamplerPeriod affect performance?

The server is currently running as a single node on the partition, but will be clustered.