In a new entry to his blog, Till Klampaeckel looks at view rendering for Zend Framework applications and how, as he assumed it would, making a change in the automatic rendering on the views could speed things up quite a bit.
My thesis is that there's a gain in page rendering time when I disable automatic view rendering and use explicit render calls ($this->render('foo');) inside my controllers. And to cut to the chase, there is. On our app, I measured a 12% improvement using Xdebug's profiler - simple before-after-style.
He talks a bit about his setup for testing his theory complete with a customized loader as well as the platform (OS and web server) he ran the tests on. He used Xdebug to run the testing. His conclusion is a pretty obvious one - what you gain in convenience you sacrifice in performance.