Using a non-blocking server with Python does not really make sense since most libraries in Python are blocking by nature and gevent only solves the most simple conversions by monkey patching (and like the author notes this is very error prone).
If you want to use non-blocking in Python then using something like Twisted is an option since Twisted implements most things in an non-blocking way, but Twisted hasn't really gained that much traction in the many years of its existence.
So yes if you do a hello world benchmark then you get a 4x speed improvement, but if you do any library calls (such as doing a MySQL query) you will get decreased perfomance since the MySQL Python library is blocking (and most other libraries are blocking as well)...
If you want to use non-blocking in Python then using something like Twisted is an option since Twisted implements most things in an non-blocking way, but Twisted hasn't really gained that much traction in the many years of its existence.
So yes if you do a hello world benchmark then you get a 4x speed improvement, but if you do any library calls (such as doing a MySQL query) you will get decreased perfomance since the MySQL Python library is blocking (and most other libraries are blocking as well)...