The impedance curve of the speaker will matter more than efficiency. Efficency determins loudness but impedance curve can determine the amount of distortion.
Most SET amp have high output impedance that will interact with speaker impedances. So you want to look for for a steady speaker impedance > 6 Ohms through out frequency range with low phase angle. Every speaker manufactor should be able to furnish you with this information.
Most SET amp have high output impedance that will interact with speaker impedances. So you want to look for for a steady speaker impedance > 6 Ohms through out frequency range with low phase angle. Every speaker manufactor should be able to furnish you with this information.