Fbodfather told me months ago that the Z/28 would shine on autocross. So I think with the gearing and what not they didn't expect it to absolutely blow away the ZL1 on Nurburgring, but it probably will on autocross or especially shorter tracks with more turns.
That being stated, nothing is cooler than a 427 Camaro. So if I could, I would add a Z/28 to my garage. But not replace my ZL1 with one.