The answer is really that it's complicated. The issue isn't just a matter of power and current but the speaker impedance and how the amp interacts with it.
Some speakers may have a dip in the mid bass, causing a dip in amp output. Well, that may sound really good to your ears! :)
My suggestion is to always listen to an amp/speaker combination, at levels you actually like to listen at.
However, if you want to study this further, take a look at how Stereophile measures amplifier response, especially tube amps and the simulated speaker load.
Some speakers may have a dip in the mid bass, causing a dip in amp output. Well, that may sound really good to your ears! :)
My suggestion is to always listen to an amp/speaker combination, at levels you actually like to listen at.
However, if you want to study this further, take a look at how Stereophile measures amplifier response, especially tube amps and the simulated speaker load.