@Phalcon: It's a media sharing website, has basic Youtube like tasks and some back-end processing (update views stats in batch, logs, search suggestion logs). I see that I'm over-optimizing at starting point because maybe my site won't reach very high traffic level. But I really want to pursue the terms "High Performance" + "Efficiency", and further more, I can minimize the server costs which is very expensive in my country.
@Nikolaos Dimopoulos: thank you for your answer. I have recently tried to install HipHop VM, it's require some time-consuming workaround for upgrading gcc compiler to a new version even if I want to use pre-built packages. I just not quite sure about moving from Symfony2 to Phalcon. Symfony2 has a large community, and stable bugs tracking, fixing process. And after a couple months study about it. I know it can allow me to easy develop my application's future features. Phalcon is quite new to me, fortunately its syntax is quite similar to Symfony2. Now, I just wonder, is there any lacking common features compare to symfony2? Or something that I should notice when moving current Symfony2 codebase to Phalcon?