I suppose it depends on what exactly is meant by "data science." If find that for stochastic simulations, C++ and the Eigen library are unbeatable. You get the readability of high-level code with the performance of low-level code thanks to the "zero-cost abstractions" of Eigen.

If by data science you mean loading data to memory and running canned routines for regression, classification and other problems, then Python is great and mostly calls C/FORTRAN binaries under the hood, so Python itself has relatively little overhead.