A spec showing that power doubles as the impedance drops from 8 to 4 and then from 4 to 2 may be misleading. I recall a Stereophile test report a few years back of some high-powered solid-state amp, perhaps a Classe, whose ratings indicated just such a doubling. However, the measured power output turned out to be considerably greater at 8 ohms than the rated power, slightly greater than the rating for 4 ohms, and it just barely made the 2 ohm rating. It seemed clear the manufacturer was playing a game with the specs. It had intentionally downplayed the actual output at 8 ohms just to give the appearance of doubling its power for 8/4/2 ohms.
Amplifier specs, does they matter?
For solid state designs, the manufacturers boast about their signal to noise ratios, total harmonic distortions, slew rates, frequency responses, and many others. Meanwhile, the makers of the tube amps praise the liquidity and musicality of their designs. Obviously, amplifiers with tubes don't measure nearly as well as solid state amps. So, do any of these specifications really matter?