You can just as easily say RoR is slower (than, say,
Symfony 2.0 on PHP with an opcode cache)
However, but I've found that there is lots of fragmenting in the community/documentation. See the differences between 2.3.4 -> 2.4 (lots of breaking changes) -> 3.0 (almost entirely different framework). Which is kind of a bummer when using it for long-life projects (we have a few projects are stuck on 2.3.4).
That said - Symfony 2.0 looks fantastic, and very much like the next "Rails-like" PHP framework.
They just make the framework better with every new version, although in case of Ko3 minor versions are backward compatible (for example 3.0.8 with 3.0.1., but 3.1.0 will not be, at least concerning the response object and the ORM logics).