The existing system test framework spawns off a bunch of jmxtool processes to collect metrics. This is rather heavy-weight and also, requires advance knowledge of all the beans (many of which are dynamically registered). E.g., per-topic stats pop-up only after the topics are produced to.
Since we are using metrics-core, we can just turn on the CSV reporter to collect these stats. I had originally thought version 2.1.3 had various bugs that rendered it unusable for CSV reporter, but I gave it another try and it seems to be fine. Will post some output.