You can also use the CRTMPServer to do your stress testing. You can pull the source and compile it: details at rtmpd.com.
Then run the resultant binary with the attached config. To configure it, modify the stresstest.lua. In particular, you’ll want to edit the following (all towards the bottom):
targetServer: the address of the server you want to hammer. Example: 192.168.1.30:1935
targetApp: if you are using anything other than the default live RTMP app
streams: the stream(s) you want to pull from the target
numberOfConnections: total count of RTMP streams you want the utility to pull
Aside from watching the CPU and the output of this tool (which will start complaining when it can’t make additional connections), you may also want to pull up an additional feed in JW Player or something to see how good/bad packet loss gets. That will give you a good feel on how the numbers are actually affecting the user experience.