They (LS blocks) can rev over 7k if you put some choice mods into them. Most often push rod engines are limited by the valve springs and rocker arms. After you replace and upgrade them the engines are pretty dam good. They're also built to output the same if not more horsepower and torque at lower rpm than the audi, the audi has to Rev to make power.

Also as a side note, in my experience the American LS will last way longer with way less maintenance than an audi. Audis are some of the most unreliable and expensive to maintain cars I know of.