At the intro, Ralph said that with both models, you can turn off everything except the braking assistance. The SRT Viper has a track pac option (as does the GTS). The SRT comes out lighter because it doesn't have some of the sound insulation materials, espically in the wheel wells. So, SRT model with track pac is the way to go if you like to track day your car somewhat frequently. The SRT Viper is the next gen basic Viper. The GTS is somewhat upscale with interior and sound insulation and a bit heavier. The SRT uses cloth interior, GTS uses leather.
According to Ralph, in the current Viper Nation, about half of the Viper owners track the car frequently. The SRT Viper is intended to appeal to those folks. The GTS is for the other half and also intended to capture new owners who want a bit more refinement in their car.