Regarding Python:
If you need performance for compute-intensive stuff, look at Numeric Python http://numpy.scipy.org/ and Pyrex http://www.cosc.canterbury.ac.nz/greg.ewing/python/Pyrex/ . Numeric Python is a Python extension that provides a lot of old-school numeric facilities as fast C code -- vector math (an essential tool for ANN work), etc. Pyrex is a tool that essentially allows you to compile Python code down to a native executable.
With Pyrex you need to be careful about using reflection, because it can't fully compile code that uses certain reflective constructs (notably locals() and globals()). I mention this restriction only because both AI and exploratory coding (implied by your "prototype" remark) often take advantage of reflection more than other kinds of application areas do.