Because the engine with more RPM can use lower gears (that is better than using the crank to make torque)and it has more power cycles in whatever distance you are running. Doesn’t matter if it’s 1/8th or 1/4 mile or a circle track engine, the higher RPM engine makes more power cycles. That is what matters. How many times the cylinder has a power stroke.
7k is nothing today. Even using 273 rockers you can do 7k forever. I’d venture to say that 8k if the oiling system is good is nothing today.
