Something to keep in mind about the Z/28's time at Nurburgring was it was done in the rain. According to this article GM feels that there is another six seconds in the car. So depending what Ford is basing the GT350R's time off of the Z/28 may still be faster, by one second.
Another thing to think about, the new Mustang is just finally catching up to the outgoing Camaro.
http://www.roadandtrack.com/new-cars...rburgring-lap/