i doubt a le mans gt car would be quicker.
Bmw m3 gt2 specs are 2860#, 470 horsepower
sprint cup 2013 car is 3240#, 900 horsepower
thats a huge difference in handling on the straightaways, and would presumably offset any advantage the current gt2 would have in the corners, which i doubt would be as significant as you would think. there is a ton of money and smart ppl in the series, second only to f1 in that regard.