Brandon Williams has been doing some testing on the garbage collector options we are using, and found that removing the line
-XX:CMSInitiatingOccupancyFraction=1 \ from bin/cassandra.in.sh dramatically increases throughput by reducing the amount of CPU used by the garbage collector. This will be part of 0.4.2 and 0.5, but in the meantime, thought you'd like to know. -Jonathan