Umm...engine size really has nothing to do with it. Your RPM at a given speed is dependent on the transmission, differentials and wheels. But normally you'll see different diffs or tranny gear ratios on a bigger engine in the same car to take advantage of the power curve.

 

To clarify; engine size does have something to do with it. The engine determines the amount of power produced and the cars are geared accordingly. Bigger engine makes more torque down low so they are geared to cruise at lower RPMs. Moral of the story is yes you should be cruising at over 3000 RPMs in your Audi. Its engine makes its power at higher RPMs primarilyaround 3000 because of the turbo thus your car is geared to cruise at those RPMs to maximize the ease of freeway driving and maintaing higher speeds.