I have a different Hankook tire in that size (the front size, 245/45/17), and on a 9 inch wide rim on our cars, they are too small. They might look better on a narrower rim, and on a Mustang, but if I could go back and do it all over again, 255/45/17 or something else.
Mine (Ventus HRII) have the same 340/A/A rating, I have gotten good wear out of them (too good, I want to wear them out to get something that fits our car better, they aren't Mustangs). I get goo forward traction and not much hydroplaning, but stopping in the rain isn't as good as I had hoped.
97 Mark VIII LSC/Silver/Gray leather
97 Cougar 4.6 Sport/White Opalescent Tricoat Metallic /Gray leather down but not out?
89 Cougar LS 3.8/Oxford White/Gray velour/HG need replaced AGAIN
00 Grand Marquis LS/Vibrant White/Gray velour
63 Falcon 302/black and rust/shed isn't moving
82 F-150/Oxford White/dumb VV carb doesn't pass emissions