As others above have said I don't think that aspect is very important , even in a large room and at lease braking levels .Well, I'm of the opinion that it matters based on what I've experienced in my system using speakers that had an uneven impedance curve.
Tmsorosk (System | Threads | Answers | This Thread)
Relating back to what Unsound stated in his previous post, the reduced power output into higher loads (lower impedances if I'm reading Unsound correctly) from an amp that does not double down (double power as impedance is halved) resulted in a sound that was always "bright" because less power was being delivered by into the mids and bass frequencies than the treble frequencies. Therefore, there was a higher decibel level in the highs than in the mids and bass. The difference was not large, and it probably wasn't noticeably measurable on a Radio Shack decibel meter, but the results were clearly audible on my speakers that had an uneven impedance curve.
Once I drove them with an amp that doubled down, the sound was evened out and the speakers no longer sounded "bright".
FWIW...

