"Replacing the previous (and highly recommended) Z51 packageóit added larger wheels and tires, a stiffer suspension, bigger brakes, and shorter gearing to the base Corvette coupe or convertible"
"As for the mechanicals, the Grand Sport keeps the base carís 430-hp LS3 V-8 (436 hp with the optional exhaust) and steel frame but gets lots of Z06 bits, including its much larger tires (275/35-18s in front and 325/30-19s in back), wider track, cross-drilled brake rotors (14.0-inch fronts and 13.4-inch rears), and visual add-ons (front air inlet, bulging fenders, and rear brake-cooling ducts) that go more than skin deep, as they reduce aerodynamic lift by half."
And according to GM it's 2 seconds quicker around it's 2.9 mile track than a Z51. 2 seconds on a small track like that is not bad at all. While not a Z06 it is half the Z06's advantage for alot less than half the money difference.
2000 Red 1SC Z28 A4 - dead for now
2005 Black GTO M6 6.0 - Split daily driver
1987 Silver Fiero GT - Split daily driver