From Matt Porrit at Catalyst:
A small quote:
The tests used Apache Benchmark to request the "My Home" page of a Moodle 2.9 instance 10,000 times using 20 concurrent threads. For the tests we also disabled Operational Code Caching (opcache). This is by no means reflective of a real world use case for Moodle, but for this test we just wanted to see the performance difference that PHP7 may deliver over PHP 5.6 in the request, compile, return cycle. The only difference between tests runs was the version of PHP.
The graphs above clearly show a performance increase for PHP7. PHP7 completed the 10,000 requests 12% faster than PHP5.6. With 95% of requests taking 16% less time to complete with PHP7.
These basic tests don't hit the 25% speed improvement touted and it is a long way off 70% faster. However, achieving a 16% performance improvement is still a very good increase for a web application.