Operations Manager 2007 Performance and Scalability
Operations Manager 2007 Performance and Scalability guide has been updated to include ACS. They have included a nice script that counts the local security events per second on a computer. The script can generate a .csv file to perform calculation afterwarts on the results.
The performance and scalability guide is available here
Notice that the official tool for performance and scalability will be the System Center Capacity planner .