Facebook's HHVM team just completed their first performance lockdown, which they spent focusing on the performance of open-source PHP frameworks under HHVM. The achievement which they chose to highlight in their blog posts is a gain of 19% in their MediaWiki performance benchmark, which is – you guessed it – a parse of the Barack Obama article.
https://code.facebook.com/posts/902199373155728/-inside-the-hhvm-lockdown/
http://hhvm.com/blog/9293/lockdown-results-and-hhvm-performance