Cassandra response time was increasing with load to a certain point where clients started to timeout and the video playback completely stopped.
After these changes, we were able to achieve a latency in the order of 10ms for our 99% percentile.
You can send metrics from Cassandra to graphite http://www.datastax.com/dev/blog/pluggable-metrics-reporting...
Since the streaming is similar to HTTP page flow, it's not that hard.
Ex: http://blazemeter.com/blog/how-load-test-http-live-media-str...