You'll win if your car runs like it should and the Mustang is stock. I've driven quite a few.
Don't know about the 427's but the newer GT's with just a CAI, tune, and DR's can run low 13's and some even breaking into 12's with a good driver. So just be weary of them, they definitely respond well to mods.
i saw a guy at the track that couldent even brake into the 14's
the funny thing is while in the stageing lanes he walked by car and looked at me like i was stupid **** b/c i had a grand prix. so i proceded to rev on him while he was walking in front of my car, jackass. well i wish i could have lined up against him because i ran a 14.6 to his 15.0
sometimes i really hate mustang guys.