This is not strictly about Ruby vs Python. Having used Pyramid (+SQLAlchemy) and Rails, I think the former is plenty fast enough such that no user cares about silly optimization, while the latter is the opposite.
Loading the Rails environment is just too slow, thus you need a preloader such as Zeus or Spring. And then you need something like Guard to make unit testing semi-bearable. But running the whole test suite would still be too slow, so you need parallel_tests to spread the tests across multiple cores (and multiple databases). And finally you drink the PORO kool-aid and start decoupling your codebase from Rails stuffs, and end up debating with DHH in HN.
Loading the Rails environment is just too slow, thus you need a preloader such as Zeus or Spring. And then you need something like Guard to make unit testing semi-bearable. But running the whole test suite would still be too slow, so you need parallel_tests to spread the tests across multiple cores (and multiple databases). And finally you drink the PORO kool-aid and start decoupling your codebase from Rails stuffs, and end up debating with DHH in HN.