Many of these questions are heavily dependent on the OS you're running and the filesystem used, and of course the heavy emphasis on Python makes it hard to make good guesses if you've never written a significant amount of it. I mean, I have no idea how much attention was paid to the development of Python's JSON parser; it's trivial to write a low-quality parser using regexes for scanning, OTOH it could be a C plugin with a high-quality scanner, and I could reasonably expect 1000x differences in performance.
Interpreted languages tend to have less predictable performance profiles because there can be a large variance in the amount of attention paid to different idioms, and some higher-level constructs can be much more expensive than a simple reading suggests. Higher level languages also usually make elegant but incredibly inefficient implementations much more likely.