yes they're efficient. They will do between 1600-1800 watts at 2 ohms. at 14.4 volts You can drop them down to 1 ohm with a good electrical and get around 2100-2300 watts.Great amps and very powerful. You got the wrong info on the zx2500.1 as well. Those will do between 2600-2900 watts at 14.4 volts at 2 ohms. I have a zx1500.1 pushing two Mag 15's and i couldn't be happier