PHP CMS Website
When you begin a new web project using PHP(and likely mySQL), it makes real sense to use the right tool for the job. In this situation, the tool refers to the application that will be the heart of the project. Since the project at hand will be a CMS, I will exclude any PHP Framework like Symfony or Zend, and focus entirely on content management systems.
Now that the discussion has narrowed to a CMS, this can be split between open source, commercial and proprietary.
In general terms, most open source content management systems(CMS) are free and include household names like WordPress, Joomla and Drupal. They are all very popular and can be used to create websites both large and small. If you plan to specialize and use one of them for multiple projects; you can become efficient with using them. However, you could find that they are not coded as lean as you would like and can actually cause more hours of work for smaller projects.
As time went on and my experience with these systems had passed, I began to notice many undesirable reasons for using these systems. For one, the web had too many bots that would hit or target these systems; before and after exploits had been exposed. Bots do slow a site down and many will hit urls that will update your database or send email to you from comments and registrations. You will have to make customizations to keep out the crap.
In addition to that, the filesystems were so huge and changed so frequently that they became a good hiding place for malicious files. In other words, if a malicious file could access a database or the filesystem, it could be hard to find in the rat's nest of a large installation. At this point, you would have to monitor them yourself with custom scripts. So, when you receive the email from your ISP about a Joomla or WordPress exploit, your unforeseen workload could stare you right in the face.
As a hand-coding PHP developer, I preferred to just code PHP and mySQL without having to create plugins and extensions. When one file could do the job, I could have ended up making four. I did not like doing more than I had to.
Now, for something really undesirable. As time marches on, a CMS version will die and not have any more security updates. In addition to that, new PHP updates on the server will spring errors on pages since the CMS site could be using obsolete PHP functions. Now, there is some serious update work. For some, this could be a good resource to pull more dollars from the clients, while others will find this horribly inconvenient. Also, as versions are updated, old installed extensions and plugins could fail too.
Although the above spiel can sound a little negative, it is something to consider for the short and long run. If you plan to build a website with endless possibilities and so that your clients can update the website, you may want to go that course. If the website will not grow immensely and needs specific coding, you may want to go a custom route.
Although some performance specs had been mentioned above, you could always tune your server and use a strong caching system or a proxy like Varnish or Squid. Varnish will help to make a slow site very quick.
Finally, if you still plan to a CMS like WordPress or Joomla for your website, you could custom code PHP / mySQL. With WordPress, you can create a template file and add pure PHP / mySQL into that template. With Joomla, you could copy the source code from your web page and place it in a subfolder. Then, you could code anything you want into the '.php' file.
A commercial CMS is a product like Expression Engine. They cost a few dollars and come with support. Some can cost under $100 and some run over $10,000.
A proprietary CMS is an in-house coded CMS that is used by a company. It can take quite some time to code, but it can have many advantages such as performance, faster completion times and allows you to code within your desired style. By contrary, an open source CMS will have its own methods for customizations and you would need to work within these limits.
From experience, I was lead to the path of creating a custom proprietary CMS since I wanted much better performance and a system that could build a web page in record time, and be easier for a client to use. In addition to that, I wanted to be able to move an HTML / CSS / JS website into a CMS very quickly. Since CMS' like WordPress and Joomla were my previous systems of choice, I would make sure that the results I wanted would be much simpler with an in-house solution.