I took a program that used to take multiple days to run in python/numpy/scipy/pandas moved it to julia... and got it down to just a few hours. Something like a 20x speed improvement. It seems the biggest speedups are gained if you happened to have implemented custom functions in python since those cannot take as much advantage of C numpy/scipy/pandas cores. That said, I still find numpy/scipy/pandas more natural. But that's probably simply because I'm more familiar with them and python.
