http://blog.stuartherbert.com/php/2008/04/19/using-mpm-itk-to-secure-a-shared-server/
To benchmark mpm-itk, I used Apache s ab benchmark to load a simple phpinfo() page 1,000 times. I ran the benchmark five times, and averaged the results.
mpm-itk: average of 37.01 seconds
mpm-prefork: average of 6.21 seconds
mpm-itk benchmarks much better than suexec and suphp, but is still quite a bit slower than mpm-peruser.