You mentioned in your 12:16pm post "...all other things being equal". Am I correct that you are also speaking of the *sound pressure level*? I ask because if so, again it would seem to me that higher speakers impedance (say 16 ohm instead of 8) would mean that one would need to raise the volume/power to achieve the same SPL, and hence in so doing could increase distortion if the amp is not operating in its "comfort zone".The 'all other things being equal' is meant to suggest that if you could magically have the same exact speakers, differing only in impedance.
16 ohm speakers do not need more power. Impedance and efficiency are two different issues; a watt into 4 ohms is the same sound pressure as a watt into 16 ohms 'all other things being equal'.
If you are used to the sensitivity spec rather than efficiency, then the 16 ohms speakers might seem harder to drive. This is because the sensitivity spec is based on voltage (2.83 volts) rather than power (1 watt). Into 8 ohms the two are the same; into 4 ohms the power is 2 watts if the voltage is the same, and into 16 ohms the power is 1/2 watt if the voltage is the same. This can make the higher impedance speaker appear harder to drive, but if we are talking about tube amps, they are no different; in fact quite often a tube amp will make more power into 16 ohms rather than less.