A company I used to work for has spent 30 years trying to migrate FORTRAN code to C. I was not involved in the project, so I don't know the details, but the gist of what I was told is that there are edge cases where FORTRAN stomps C in every performance metric. So you can make decent progress for a while, but you'll eventually hit a major roadblock that halts progress.
I think of the BLAS algos as being very Fortran friendly, and the Fortran references never _out_perform the C implementations. (The asm implementations are of course the best.)
Be curious to know what you're thinking of here.
I've no personal experience, but people historically point to pointer aliasing as the primary thing that speeds up Fortran code vs C.