Considering that I normally listen at around 85db or so, which most people think is loud, I usually have over 20dB of dynamic range in reserve. An inspection of a typical modern CD analysis indicates about 6db of dynamics on average. Much of my jazz sports peaks of about 8 or 10db, but still with average power available for distortion-free peaks over 105dB, I am in good shape.
Remember these are SET tube/valve amps and they are capable of driving a dead short at rated power, so impedance variances across the spectrum are not much of a challenge at all. The speaker drivers themselves are highly efficient and my openback enclosure configuration makes them almost resonance-free.
BTW, when I want to shake the floor with some Pink Floyd and dance around like a spaz-case or rock out to live recordings, I put a CD in my DVD player and crank up my movie rig, which would be more like normal solid state power amps everyone else is used to at one hundred watts per channel, plus a thousand watt subwoofer system on the LFE channel.
