Duke makes an excellent point that all of us should pay attention to:
Personally I place a high priority on low-level articulation even if the speaker is going to be played at high volume levels, because there will still be lots of low-level detail going on. And in my experience a speaker that still sounds good at very low volume levels is less likely to become fatiguing over a long listening session, so I encourage listening at very low volume levels as part of a thorough audition when you're speaker shopping.