Every app I had a chance to work with, written in .NET was slow as hell. OK, there's a database layer also (MSSQL) which makes it slower, but in general, .NET is not a champion of speed. Java was advertised as a queen-of-all-speeds, but, as it turned out in most cases that does not stand true or it does with 128GB of RAM and 20+ CPU cores with every level of caching possible.
Like we all said - Phalcon is the best choice in terms of performance if you're using PHP as your middleware. And not only performance, that's very important thing to note, with Phalcon you get a great toolset out of the box too.
IMHO it is also important to note how you set your environment. App server (PHP-FPM) needs to be separated from a web server (nginx). So regular Apache + mod_php
is far from the best option to scale.
If you need raw speed, go for ANSI C then. Nothing can beat that.