I recently moved from 5.6 to 7.0. Before, it was only possible to make 1,25 REST-API-Requests from a Windows-Program. Now, after switching to 7.0 it is 5 times faster.
Also the request-time is much lower, from ~1300 ms to ~250/300 ms.
Hope this helps. But no, I have no real benchmarks. But go for 7.0! You could use a docker image of php7 to test the speed.