ya they would be fine but better safe then sorry.... i work in a tire place and your not suppose to put on less then what they recommend as in the speed rating ........ but hey its not my car or i'm not driving it go for it :D
what year and model stang you have? if you have a gt more then likely it calls for a ZR rated tire (which is the speed rating) and those are rated HR'S and shouldn't be put on your car just to let you know
there is no best exhaust...... when it comes to exhaust it's down to taste what you like best
edit: well with catback mostly and hpipe or x-pipe sorta headers are a different story