Kinsta recently performed some benchmarking on PHP7 and HHVM with various CMSes and frameworks. A notable result is that Drupal 8 handled 917.10 transactions per second on PHP7 (and 1739.28 on HHVM) under their testing.
During the Drupal 8 development cycle, there has been a lot of focus on improving performance out of the box. It's obvious that these efforts have paid off in spades. One of the biggest improvements has been the Dynamic Page Cache.
There is still room for improvement, but the current performance gains in Drupal 8 are a big part of why we recommend upgrading to Drupal 8 as soon as possible and starting new web applications on Drupal 8 now.