This is exactly why I decided to use PHP for my startup. I have something along these lines that I hope to blog about in the coming weeks (I tested php-fpm on nginx/go/node.js/silk.js and php won by a landslide when it came to speed).
I would love to see php-fpm on nginx included in this test.
When it comes to speed, considering you are using nginx, the way to go is using nginx as an app server not just fastcgi frontend. Lua-nginx-module combined with proper database module (async with connection pool support like ngx_drizzle or ngx_postgres) can give you speed. OpenResty provides the simplified preconfigured way to try it and adds some features too. http://agentzh.org/misc/slides/libdrizzle-lua-nginx
The problem with php is that it looks great on (some) micro-benchmarks, but on real apps under real sustained load it certainly turns to cold dog shit from time to time for no apparent reason.
What are you basing this on? I've been using PHP for well over a decade in high load environments and never experienced it turn "to cold dog shit" .. any issues I have experienced had a good reason, not "no apparent reason".
But then, I've never used a PHP framework in all the time I've used it .. maybe that has something to do with me never having had negative issue with PHP.
I would love to see php-fpm on nginx included in this test.