Not sure how efficient your looking for but i have done the Klipsch LaScala thing for years and was happy after some modifications i.e. damping of horns, upgrading the crossovers and drivers etc.
The one speaker that gets overlooked here mostly due to being British is the Living Voice line up. I've had an earlier version of the Avatar 2 and was very impressed with the sound. They range from 94-95db at 8ohm, easy load for tube amps as they were designed and voiced off AudioNote Japan's Kondo amps. highly recommend them if they are efficient enough. Drove mine with 300b tube amps but they really like a little more power maybe 20-25wpc.