Chances are that you have 245/45R19 with 8.5" wide rims if you have the original tire size standard on the 2011 GT.
The widest RECOMMENDED tire on an 8.5" rim is typically a 255, which is approx. 10.2" wide.
The 245 which came as standard with your car is approx. 9.6" wide.
(Tire widths vary a bit between mfrs,what their profile is, and the rim width they are mounted on.)
Not a dramatic difference in width.
The profile would be based on whether you maintain the approx same tire diameter, and what width tire you choose.
For example, the closest tire diameter, with a 255 width, would be a 255/45-19, which has a dia of approx. 28" and a 4.5" profile.
If you have the standard 245/45-19, it would have a dia. of 27.7" and a 4.3" profile.
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