Symfony and Zend might perform even worse. At least Zend's bootstrapping is even heavier. The sheer number of files that have to be loaded from disk on each hit is appalling. Hence I mentioned in another comment the opcode cache (ex. APC) requirement and how every serious PHP app utilizes it.

Zend and Symfony are probably the leading OO MVC frameworks for PHP.

I'd also like to see a "light" framework meant for building APIs, like Slim, for instance.

It was simply what we have seen most often in our experience. We've got Zend as a next target for PHP frameworks. We can also put Symfony on the list.

We'd also love to have anyone who has production experience with those to contribute a test for them. The test should be fairly quick to write.