There are a lot of great posts and case studies about weather.com, which is a solid example of drupal in a high performance environment.
Performance has been a specialty for me in my own drupal career. Drupal 8 is a whole new ballgame, though. Cache tags are built in from the ground up, and the page render/caching engine is built to mimic a reverse proxy. Rasmus Lerdorf (creator of the PHP language) benchmarked a pre release of drupal 8 at >2500 page views per second with 20 concurrents.
Performance has been a specialty for me in my own drupal career. Drupal 8 is a whole new ballgame, though. Cache tags are built in from the ground up, and the page render/caching engine is built to mimic a reverse proxy. Rasmus Lerdorf (creator of the PHP language) benchmarked a pre release of drupal 8 at >2500 page views per second with 20 concurrents.