Get the Z if it's speed you want.
May '98 issue of GM High Tech got 13.11 @ 107.4 out of their bone stock 6-speed '98 Z-28; 13.07 @ 106.4 with Mickey Thompson DOT Sportsmans. Of course, the car was driven by Evan Smith who is known around the GMHTP and some Ford magazine to be able to drive the hell out of stock rides. He got high 11's out of a stock Viper GTS.
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What is best in life?
"To crush your enemies, see them driven before you, and to hear the lamentation of the women!" -Conan