What kind of mods are done to the car to require this level of extreme in the tire department?
Also, I have had some wild experiences with RWD higher hp cars and sexy tires. I remember my LS1 F-body that I had F1GSD3's on. Really good tire for the era, actually. I was getting ready to sell it and threw some Firestone Firehawk Indy 500's or some such on it...and insanely, they hooked like nobody's business. It literally wouldn't even chirp them on hard 1-2 shifts anymore. I ran a guy in a Mach 1 (4.6L) and every shift he lost about 1/2 a car to wheelspin while my WS6 just hooked. It was unreal. Cheap trash tire...but man. So what I'm getting at, is that while I normally am a fan of just throwing the applicable Michelin on, maybe hit the mustang specific forums for this. You might find some oddball hidden gem like I did.