I'm not sure what "full fat" means, but compared with current gfortran in my experience, ifort is incorrect by default, surprisingly unreliable, and typically g

I'm not sure what "full fat" means, but compared with current gfortran in my experience, ifort is incorrect by default, surprisingly unreliable, and typically generates similar speed code at the 10% level. My all-free software build of a quantum chemistry program was reported to run faster than an all-Intel libraries one on a cluster which has faster processors but is otherwise very similar to ours. If you just write in Fortran, you don't have to have to debug two versions.