According to the "operating line" graph published by Toyota at intro of the 3rd generation, 2000 RPM corresponds to only about 26 horsepower; about 2250 RPM corresponds to 20 hp. That probably varies with factors like temperature and speed. There's a hill near here that I try to ascend at the top edge of the "eco zone" (i.e., as high as possible with "ECO" showing above the HSI display). That usually results in almost or barely maintaining constant 40 mph, and engine speed near 2000 rpm, but sometimes lower. Try staying anywhere near 2000 RPM on a busy highway in the very hilly parts of hillier states!