Hey Dave,
The 08-10 side exhaust systems sell for $400-$600 typically. They offer less heat; better sound and a 5-peak hp gain on the 03-06 models.
There are numerous options for a cat back system. The Gen 4 (08-10) model differs from the Gen 3 and many Viper owners do not understand the difference. The Generation 3 Viper (03-06) came with a "crossover" exhaust system. This exhaust exit system had pipes that crossed over under the car from right to left. The left side exhaust exited out the right and the right exited out the left. The system also included an "H" pipe the connected both sides together. This "H" pipe system smoothed out the pulses of the engine and helped scavenge the exhaust pulse at higher rpm. The system was necessary to reduce noise emissions and allowed the car to pass noise regulations for new cars. The system had some drawbacks, primarily heat. The exhaust system on the Viper is encapsulated in the bodywork of the car, with very little airflow over the exhaust, the heat from the exhaust system (primarily the catalytic converters) was transferred into the cockpit of the car, the crossover system allowed the heat from the exhaust to surround the occupants, making for a toasty ride.
In 2008, the Generation 4 Viper excluded the crossover exhaust system. The new VVT camshaft softened the low rpm exhaust pulses, with less exhaust duration the engine became quieter and did not need the crossover to pass exhaust requirements. This freed up some power and reduced heat in the exhaust system.
An interesting fact we learned on the Gen 4’s is the earlier 03-06-crossover system with headers and high flow cats will make much more torque than the standard side exhaust or aftermarket exhaust. The "H Pipe" allows the VVT to work better at upper rpm and provide much better midrange torque out of the corners.
My 2 cents.