we have a 2008 zo6 vette and 2008 cobra stang that is modded and it still dont come close to the zo6, the new stang dont stand a chance to hang with it.
If you are talking power-to-weight of course...
What I was getting at is for the same money, the GT500 will be faster in the 1/4-mile (same with about any Mustang). Does it take 100rwhp more for the GT500 to hang with the Z06, yes but bang-for-buck the GT500 still wins...
Either can be faster, it just depends how much money you want to spend on each.