What is the best language or webserver to build HIGH Performance REST API [on hold]

Currently i have a REST API build in phalcon , fast-cgi and nginx.

I want to build my REST API for high performance. Like in future i will acquire 100k users in total and almost 30k live users which perform thousands of api call per seconds.

My Questions

1. I know at 4core , nginx can able to handle 16k request per second. Any other web server which can able to handle more traffic at same core.
2. Which language i pick c,java,php. As this REST API is pretty simple so it's not a big deal for me to build same functions in any language.

At final i only to want save my last bit of resources. If it will require to increase server instances then i will.