Symfony2 is a very slow framework by comparison but it's also a very complete framework (if you like to have it all). Why it's slow in the benchmarks, I can't really answer but I know that the development enviroment in Symfony2 is very slow and I haven't met one developer who at hates Symfony2 on at least one level.
One framework for PHP developers that is worth looking into is Laravel. Very clean and reasonable framework. Have a look at it here: http://laravel.com/
Laravel has an amazing amount of noise (hype?) around it which Symfony2 doesn't (why?), but looking through the code and documentation it doesn't seem to hit my pain points or be... complete.
For example, it has ActiveRecord by default, so you're focued around data stores... ideal for CRUD, but then its libraries to generate and validate forms are like something from 2008.
I'm a bit bemused as I must be missing something, given its popularity. Perhaps the apps I build are not a good fit for it - I'd be keen to have your input.
One framework for PHP developers that is worth looking into is Laravel. Very clean and reasonable framework. Have a look at it here: http://laravel.com/