JBoss doesn't really play much of a part with respect to persistent http sessions. So you will need to check with the various servlet containers.
However, I don't believe there is any support in Jetty, and as you say, Tomcat's implementation is still experimental. You might try resin which is the only other servlet container that has a plug-in for JBoss. It is free for development and non-commercial use. And it supports persistent http sessions.
Of interest may also be a performance measurement of servlet containers, http://webperformanceinc.com/library/ServletReport/.
Finally, you may wish to consider session clustering, supported by JBoss as an alternative - giving 24x7 operation and perhaps circumventing the need for persistent sessions. Just a thought, depending on your requirements.