Haven't seen a stock V6 run into the 13s...so sorry but unless your track is located in a place with great air and elevation, it won't happen.
That said, we've had lots of guys with bolt on/tuned V6s run into the 13s, but again, if you are running in moderate to bad Density Altitude at your track, 13s may not happen.
The GT was faster for a couple reasons. 1) less weight. 2) more torque. 3) lower geared.
If the V6 weighed what the GT did and had the same gearing they'd be running into the high 13s stock as well. Wouldn't need the extra torque to do it.
5th gen IS SOLD! 6th gen built 10/14!!! Can't wait!!