Switched from CPython+Numpy to PyPy years and years ago, got a 60x speedup on a core numerical kernel and 20x speedup on real-world benchmarks. The codebase was a multiplayer game server. Less memory usage overall, leading to a big improvement in the number of players that could be connected.
You have to not have problematic libraries in your system, but honestly they're all either shitty on CPython too (literally every GUI toolkit that is not Tkinter!) or they're stuff like lxml, where the author/maintainer just has an anti-PyPy bias that they won't drop.
You have to not have problematic libraries in your system, but honestly they're all either shitty on CPython too (literally every GUI toolkit that is not Tkinter!) or they're stuff like lxml, where the author/maintainer just has an anti-PyPy bias that they won't drop.