Once the JL "latches" into one of it's "gears" (basically an adjustment of the rail voltage), it operates just like any other amplifier. Meaning if you connect a 2ohm load, the JL will "latch" into the "gear" for a 2ohm load, but from that point as the impedance of the speaker increases and decreases so will the output of the amplifier. It would be fairly undesirable to have an amp with truly constant power. For example, a subwoofer playing at or near Fb would be excessively overpowered if power output didn't drop with the increase in impedance. IIRC in the Carsound review the 1000/1 was only in the mid to high 60's for efficiency. Which isn't terrible, but not great either. The HD amps I believe are more efficient than the Slash series are.