Wim Leers has at least three good blog posts on the Drupal 8 “Page Cache” and performance, which promises to be much better than Drupal 7 performance. Drupal 8 now has page caching enabled by default states, “Drupal 8 is now between 2 and 200 times faster than Drupal 7 for anonymous users.”
Drupal 8’s Dynamic Page Cache discusses D8’s Dynamic Page Cache. As the article states, “The Page Cache module only works for anonymous users, the Dynamic Page Cache module takes that a step further: it works for any user.”
renderviz: tool visualizing Drupal 8's render tree provides a few more details, and also provides a demo of the cool Firefox Developer Tools 3D view. The image I show comes from that page.
As I wrote in Huge Drupal 6/7 Boost module performance improvements, the Boost module for Drupal 6 and 7 makes this website render pretty fast, and it sounds like Page Cache is a replacement for Boost in Drupal 8.