In reply to mark k..

PHP 5.6 (or was it 5.5?) integrated opcode caching into php core which eliminated the need of parsing php files for every request and reduced the amount of memory required for php application in a web server enviroment.

PHP 7.0 have improved the parsing speed but if the generated opcode is cached the parsing is not done at all and therefor in the real life you will not notice any improvement in a webserver enviroment.

People that use PHP in a command line enviroment will experience a great speedup because in that enviroment files are being parsed on every request.

Anyway, the major bottleneck in wordpress sites is DB access. DB access speed (or slowdown) eclipses any thing you do on the PHP side. You might have the fastest PHP code but with slow DB access your site will be slow.

The answer most people have to that is page caching. With page caching which is done right, (via nginx or apache 2.6+ caching directives) you are not going to even run any PHP code. If you use some inferior solution like W3TC, there is some wordpress booting involve but again if you use opcode caching it is just super fast whatever php version you use.

The other answer to the DB slowdown is object caching. Here there is some actually improvement that might be gained from faster PHP, but you usually can not do object caching in a shared hosting enviroment, and where available most people employ it as an addition to page caching which was discussed above.

So Here is a challenge, you are welcome to prove me wrong and show actual speed improvement numbers that are relevant to wordpress, with a core theme. Check it with with three scenarios - no caching, page caching, object caching based on APCu and object caching based on mecache (memcache is slower than APCu therefor it will be interesting to see the difference).

Sorry for not bothering to do the tests myself, but you made the claims, you need to show they are actually true.