The automatic knows what to do. Most people accelerate faster than what is the most efficient. The Impreza has a small engine. A larger engine might do 0-60 in 10 seconds more efficiently than the 2.0, as this would put the Impreza at max output, while the larger engine would only be operation at 70% (for example) of that or so. If you use a light foot and accelerate slowly, the automatic will behave accordingly. If you use a heavy foot and accelerate quickly, the automatic will behave accordingly.