This sort of thing is pretty difficult to answer precisely, I think your numbers give you a general idea, however other effects of optimization may still have an effect, depending upon how your code is structured. Obviously if you write code that the compiler determines is unnecessary, as in the case of your benchmark, that will change things substantially. If you are working with arrays that exceed your working set size, then again, this may "equalize" things a bit. Ultimately what you are shooting for is to write things as efficiently as you can, then use a profiling tool to see where the fat is for further improvements. There likely will be some hardware dependence as well for these relative timings.
One minor note, your EXP appears to be quite a bit more efficient relative to addition than on my setup.