Is there any sample software available for a 256-point complex FFT
radix 4 and radix 8?  Are there any execution times available for
these FFTs?

Software is currently being developed for radix 4 complex FFTs for the
DSP56001 but not radix 8.  Better performance should not be expected,
however, as our DSP hardware is optimized for radix 2 FFTs.  It should
perform about as well as FFTR2B given zero wait-state memory but will not
be as fast as FFTR2E.  FFT algorithms are found in Dr. BuB as free,
DSP56000/1 general purpose software.