I've had few problems scaling my Rails site up to over 2M requests per day. The "Rails can't scale" stuff is a myth. Good code, with proper techniques goes a long way.
...when you need to dig into the Rails source to figure out what's going on. You really need to fully master Ruby to be able to grok Rails source well.
I think both languages have easy enough C binding.
Rails is the bomb, except when you need to scale, or something is wrong.
Python by far has more modules, and ties into C easiler (and C++ via weave).