It will be nowhere near the GT which has 460HP. It's barely stronger than the motor that's in it now which is 310HP turbo. You could get the 3.31's in it now, so they added 20HP and put an available 3.55 gear for it.... In Mustang land, this isn't really big news as much as the soon to be 4 door and AWD versions are.
4.5 0-60 is nothing to sneeze at.