PyPy is really impressive, I love the idea of getting all these optimisations (SIMD, STM) for free... but as you say, numerical work means numpy, scipy, pandas, which don't work with PyPy. Even if the NumPyPy project was able to fully match the Numpy api, you still have a lot of large projects like Pandas that depend on the c api. it would be stupid to copy everything. Perhaps something can be worked out between pypy, cffi, and cython.

In the short term Numba is much more practical for numerics. In the longer term Pyston looks promising - it's actually similar to Numba in that it also uses LLVM, I imagine there could be synergy between the two...