Artur Graniszewski has written up a comparison of the performance of a standard Durpal 7 installation using HipHop versus APC to handle the optimization of the application.
There have been many suggestions on improving Drupal performance, some of them recommend the use of APC module, data caching, or even compilation of the entire system through HipHop for PHP. While the first two solutions have been successfully implemented, no one was able to perform the build process. After many battles with the the compiler and the Drupal code, I present you results of the first successful translation of Drupal 7 to C++ language
He introduces the methods he used and the statistics of the platform (hardware) he tested with. He also includes the software used and compile commands used to create the compiled Drupal version. Included in the post are graphs showing CPU usage comparing the two types of testing (HipHop and APC) versus a normal PHP-based installation. It also briefly touches on concurrency levels and the different optimizations that could be made with the gcc compiler.