I agree, more tire is needed, 285 would look good on 9.5 in rims, but those are 10.5 in, so at least 315... I would've paid the extra buck, I think it would have given your stang a more muscular look... just my thoughts...
anyways, what you have there with those back tires, is a pretty good "difting" set-up... I bet your car slides more now...