None, on purpose. We want maximum portability, and so the Rails defaults are Ruby-only on purpose. Of course, it's easy to add gems that replace things that are written in C or Java, depending on what makes the most sense for your platform.
Would it make sense to submit a rails-optimized pull request for this benchmark that replaces some key performance bottlenecks with appropriate C gems? I'd be curious to see how fast rails can go out of the box without doing your own hand optimization.
