title: What's the best PHP framework for a large, high traffic, feature rich web app?
body: <p>I know there's a million "what's the best PHP framework" questions out there, but it seems like the answers tend to be skewed towards rapid development and low code bloat. We're looking to rewrite a very large, extremely feature rich, very high traffic web app, so our needs are pretty much the exact opposite. In order of priority, here's our needs:</p>
  
  <ol>
  <li>High Performance - Lots of complex DB operations, very high traffic.</li>
  <li>Feature rich - if there's a technology out there, we're probably using it somewhere in our app.</li>
  <li>Customization - there's a fairly good chance that we'll need to overwrite some of the functionality of the framework. From what I've read this is easier in some frameworks than others.</li>
  <li>Low learning curve <strong>OR</strong> lots of knowledgeable developers - we're growing, so we need to be able to get new people up to speed quickly, or we need to be able to hire people who are already familiar with the framework.</li>
  <li>Built in testing framework - I'm kind of new to this area, but this is a direction we want to move to streamline our QA process.</li>
  </ol>
  
  <p>So, what say you? Codeigniter? CakePHP? Zend? Symfony? Something else entirely?</p>