a passion to perform ;)

Hi, i just benchmarked some of my applications with PEAR::Benchmark and would like to know if any of you have good literature regarding PHP and performance in generall? I am not talking about precompiled scripts (ioncube, zend, ..) Basically I am trying to find out how good a standard HTML rendering PHP-Applications usually performs? Furthermore I wonder of there are any usability papers/studies regarding this topic? (how long is long for a user? how long is a user on broadband usually expectin a page to load without thinking "damn. why does this take so long?") Maybe anyone knows of a good free performace and memory profiler? Yours, Matthias