In a new entry to his blog, Fabian has posted a patch he's developed help get things running faster with Symfony and Propel:
I found the sfBuilders that are responsible for stripping the comments from the generated propel classes and also saw that there is a addIncludes parameter in propel.ini. Lets reuse that and modify the Builders to strip the inline includes and requires.
What he describes as a "tiny step" can help you squeeze that much more performance out of your Symfony application. You can download the patch file here.