I have a system currently written in Python that can be separated into backend and frontend layers. Python is too slow, so I want to rewrite the backend in a fast compiled language while keeping the frontend in Python, in a way that lets the backend functionality be called from Python. What are the best choices to do so?
I've considered cython but it's very limited and cumbersome to write, and not that much faster. From what I remember of Boost Python for C++, it's very annoying to maintain the bridge between languages. Are there better choices? 
My main factors are:

speed of execution
speed of compilation
language is declarative
If you used Jython you could call into Java back-end routines easily (trivially).  Java's about twice as slow as c and 10x faster than python last time I checked.
Language choices for writing very fast abstractions interfacing with Python?