IMO, acceleration performance of Z06 and GTR shouldn't be measured by 1/4 times as these two cars are very different.
Generally:
0-100 mph: GTR>Z06 (AWD, short gearing, better tires and seamless shifting from DSG overcompensate for the lesser P.W.R & T.W.R);
>100 mph: Z06>>GTR (greater P.W.R & T.W.R becomes critical)
Rolling start (generally): Z06>GTR
And what's all the fascination about straigtline perfomance anyway? I personally don't care if one car does 1/4 faster than another (you can perform approximate calculation and tell that without the actual run anyway). Race track - that's where you learn the true worth of the sportscar!
