I really don't like putting an actual "horsepower" number on a product. A 300-hp vehicle launching on slicks and a transbrake will put a rearend through more abuse than a 600-hp car on street tires. It's not really the engine torque, it's the flywheel inertia and how hard your hitting the tires that's going to break something. The greatly simplified answer is that street tires aren't going to hurt the suspension. It comes down to how serious are you about drag racing your car. If you're planning on lifting the front wheels on launches and your sanctioning body rules let you run something besides the orignal leaf springs, a parallel four link would be a much wiser choice.