Scaling
Handle 40x as much traffic -- Switch to Drupal 8 [Update: ok, not so much]
[Update: It turns out the Drupal 7 site we tested had page caching disabled.
I've got a theory: The Scientific Method applied to web site performance
What can you do about this page being so slow? That's a question we've been asked by half a dozen customers in the past 6 months, and as it turns out, we can do quite a lot.