Is object-oriented PHP slow?

The most important thing to remember is, design first, optimize later. A better design, which is more maintainable, is better than spaghetti code. Otherwise, you might as well write your web app in assembler. After you're done, you can profile (instead of guess), and optimize what seems slowest.

Here's good article discussing the issue. I also have seen some anecdotal bench-marks that will put OOP PHP overhead at 10-15% Personally I think OOP is better choice since at the end it may perform better just because it probably was better designed and thought through. Procedural code tends to be messy and hard to maintain. So at the end - it has to be how critical is performance difference for your app vs. ability to maintain, extend and simply comprehend

This bugs me. See...procedural code is not always spaghetti code, yet the OOP fanboys always presume that it is. I've written several procedural based web apps as well as an IRC services daemon in PHP. Amazingly, it seems to outperform most of the other ones that are out there and editing it is super easy. One of my friends who generally does OOP took a look at it and said "no code has the right to be this clean"

Conversely, I wrote my own PHP framework (out of boredom) and it was done in a purely OOP manner.

A good programmer can write great procedural code without the overhead classes bring. A bad programmer who uses OOP will always write crappy OOP code that slows things down.

There is no one right answer to which is better for PHP, but rather which is better for the exact scenario.