A fellow named John have posted some benchmarks of the newly released GNAT GPL (20090519). They are, to say the least, very interesting. The entire post can be read here.
John compares the speed of 6 “smallish” (his own term) programs written in Ada, Fortran and C (though only 4 of the programs have C implementations). He uses two different Fortran compilers.
As expected C is the fastest language, but Ada is coming in on a very close second place, leaving Fortran at the bottom of the performance curve.