Fastest commands

Is there a list of commands or any guidance on what executes the fastest? There are some notes in some of the ereg_, preg_ and str_ function docs about which ones are faster, but what about others? Also, I want to do a replace where the search is array indices and the replace is the values of the found index. Is the following the fastest??? $content = "one, two, three"; $thearray = array ( 'one' => '1', 'two' => '2', 'three' => '3', ); foreach($thearray as $search => $replace) { $content = str_replace($search, $replace, $content); } Thanks! Shawn