CodeIgniter or PhalconPHP ?

Someone already touched on this, but if speed and performance is your only concern, then you can't get faster than just native PHP! Someone else also hit on the fact that it's not the framework speed you need to worry about, but the hardware you run it on. Hardware is constantly getting cheaper. I have fixed a few slow, overloading sites just by moving them to new hardware - far cheaper than recoding or porting!

If you want speed, then in some cases PHP has limits.  I've hit them and needed to surpass them.  HHVM all the way, it leaves PHP into the dust. 

Hardware is getting cheaper.  But then you are completely forgetting about support.  What if you have 5, 10 or 20 servers?  Will you be supporting them?  Are you available 24/7?  Will you be supporting the firewalls, loadbalancers, switches?  I doubt it, you'll probably be wanting managed support which then costs an arm and a leg.  

Design the infrastructure and software around the problem you are trying to solve.  Are you getting a million requests now?  Are you paying up front for PPC/Adwords?  Will you just be relying on SEO, if thats the case then you will either have to do it on your own or pay someone big bucks for it and it takes time and effort to rise up the rankings.

Just developing software is one part of the picture.  There is so much more to know when delivering sites when you need millions of clicks.  I know, I've gone through the pain!