Fortran -vs- C for Numerical Computing

[cn7gr8ag at ariel.unm.edu]

I need some advice on computer languages.

I'm going to be writing a large numerical simulation which will need to
be used on both mainframe and personal computers.  The program will be 
about 5000 to 8000 lines long and portable.  The basic design of the code
will be to solve a number of coupled partial differential equations for a
variety of boundary conditions.

The question is which language(Fortran or C) will provide me with the best
all around performance on both the mainframe and personal computers as well
as the greatest pertability. 

Any information on both Fortran and C compilers for the personal computers
will be a great help also.  Speed is of the essence.

Bill Rider UNM