We were doing some load testing of JBM and noticed (in our case at least) we were able to increase message throughout by 25% when we patched JDBCPersistenceManager to gzip the data before persisting it to JBM_MSG.
In our scenario, we have lots of CPU to spare, so we don't mind taking the hit to zip/unzip the data. Also, the data itself is XML and usually is reduced by a factor of 10 or more when we compress it.
Any chance of adding a "zip" option to the JDBCPersistenceManager?