Can’t really help you with this but if you figure things out it might be great to put it together with the input from the other topic I’ve created (Hoster Best Practice “Cookbook” or page) and write things down for other users in the documentation.
We started running a setup on hhvm with Flow 3.0, which is mostly hhvm compatible and the performance increase over plain php (even with php-fpm and php7-rc1) was tremendously (talking one order of magnitude).
Other than that, you should put some of the flow caches to some shared memory storage like memcached or APCu (see http://www.michielroos.com/articles/use-memcached-as-your-neos-cache-backend.html).
Well, the possiblities are rather limited without cutting on framework features…:
try “composer update -o” to create an optimized ClassMap for class loading
create a special RequestHandler that does a reduced bootstrap and doesn’t initialize parts of the Framework that you don’t need (see Bootstrap::buildRuntimeSequence): Start removing components from the end of the bootstrap sequence (sessions, resources, persistence, reflection, … in that order)
One of the biggest resource wasters is the reflection service, even with all the caching that is already applied, but unfortunately it is a dependency of persistence.