The reason I used to belive was they all sound similar, but higher impedance models are able to take in more power and produce a better sound. The frequency response would be the same for all models, but the higher impedance one is able to get better detail and clarity. But they are all about equally hard to drive, the 80 Ohm need more power than you expect and the 250 Ohm need less than you expect, so that reason is gone.