These discussions are valuable and should not be scattered on blogs that may not be there in six months time. The best place for this is either here on the development list, where all the brains are, or on the Performance and Scalability forum http://drupal.org/forum/49 A few comments: - PCRE would be faster since the underlying code is in C and hence is native to the platform. PHP is interpreted and hence slower (as you found out). - A PECL solution is not universal, since many of Drupal's users are on shared hosting where they can't fiddle with PHP's setup or download plugins/libraries for it. You alluded to this, but this is more explicit. In order to assess real penalty for the PCREs, can you try a script that executes without that part (i.e. take out the part where there is a PCRE and a callback altogether) and see what percentage improvement there is.