with mods in sig ive done more then 30 launches on my slicks and torque boxes are still fine not cracked, im going to get reinforcements as soon as possible, but dont be afraid to take it out a few times and rip her up if you have slicks.
Biggest determining factor IMO is the condition of the underbody and previous driving style. Previous abuse can and lead to flexing..and in turn metal fatigue much in the same way rust can fatigue metal.
My car was not really driven that hard and only has 56,000 Miles on it and yet my "C" pillars started to get some waves in them, when I realized that I welded SFCs in.