Were you running Silverfrost from Plato and C from a DOS prompt? For a proper test, you need to run both in the same environment.
I'm still using a version from 5 years back. That is slow compared to PowerStation, IVF, lahey, g95 or gfortran. But then again, I seldom run it outside Plato so it may be Plato that is slowing things down. I don't know about the current version.
Powerstation is MS last version of Fortran 90(produced in the 90s). You may be able to get it if you are on an MSDN subscription. That's where I found it. A bit quirky in that it open only works with 8.3 file and directory names.