Many lower resistance speakers (measured in ohms) such as the Epos (I have no experiance with them) tend to have low resistance because they designed the speaker with a focus. One cannot have low extension and efficiency without low impedance.
One thing is for sure, you can't have all three.
I would also say that you can't base a speaker's performance on it's specifications, you must listen to them youself.
The good news is, because the amp is 4 ohm stable, you have a wider range of speakers that you can potentially and safely use.