Again, we arrive at the inevitable conclusion, every design has its flaws.
For Mwilson, I have been using Lowther fullrange drivers recently and they have 98db/1watt efficiency unloaded, 100db/1watt in a cabinet. In my cabinet, they are good down to the low 40's, and they have a resonant freq of 36, so I am not "on the spike", but rather rolling off a few db above it. This leads to a rather steep low cutoff which you can either live with, or integrate a very good sub. Right now I am living with the 40Hz bottom end, and it is quite enjoyable, although there are some records that display the flaw. But, the natural tonal quality, and speed, detail and phase coherence makes up for the 1 bottom octave of missing bass response. I know some disagree with this thinking, but few audiophile speakers actually produce much below 40Hz without some rolloff. So the sound is not really lacking much compared to most others. I have toyed with the idea of integrating a pair of TL subs of my own design, but haven't done it yet. If you have not listened to some Lowther systems, then you should really try to find some to audition. A quite remarkable full range driver.