Not sure how accurate this information is as it posted over on the SVT forum. But to sum it up the Z28 in it's present form is not as fast as the ZL1, the car was getting upset in the turns due to bumps and stiffer suspension.
Posted by ThePill, who you may not agree with but he does seem to have a knack for obtaining inside information.
"there is a serious issue with suspension, handling or braking. The Z28 is REAL uncomfortable right now in corners. If that's the case, seems like Team Camaro is running their mouth before the car is even done... Simulations maybe? Either way, the way the car was running a few weeks ago, it is not breaking records as is.The car will make a revised run later this year... probably Fall '13. The ZL1 can reach over 170mph on the 3km stretch, the Z28 was about 165... The only place Chevy really seemed to mash the throttle."
2012 Ford Mustang 5.0. Brembo, 3:73s 13:07
2012 Challenger 392 auto 12:40s 112 stock
2010 SS, LS3, Cammed, LTs, NT05R,12:20s
2004 Redfire Cobra, Pullied & Tuned
1986 GT, Ed Curtis 347ci, 11:20s motor. 10:30s 100-hp shot