I hate to say it, as I love Porsche, but on a track, all things being even, I think my money would be on the Z06. The 997 Turbo is not a track car, it is a GT which can handle well. While the Z06 is a track car. That being said, wait for the GT-2's debut, that thing will most likely spank anything this side of a C-GT on a track.
As far as straight line performance, again all things being even, I think the numbers favour a Triptronic equiped 997 Turbo (0-100 of 3.4s on over boost) over a C6 Z06 (0-96 in 3.7s), while a manual 997 Turbo gets the same 0-100 as the Z06.