It depends on what you're writing. I've seen slow C++ and fast Python. Not to imply your director made a bad call; especially if you already had a reference Python implementation to check against the new C++ implementation for correctness, you can gain quite a bit depending on The domain you're operating in by swapping out a Python engine with an engine written in another language (if for no other reason and it gives you an opportunity to check all your assumptions against a system solving real problems for real people).