I bought a pair of Sennheiser 580s used for $85 last year. They have 600 ohm impedance and sound marvelous...
akg k240m >300ohms
akg k240s <
Stanton dj pro 60, totally recomended , but have 50ohms or something.
and samson c-que 8 headphome amp, its not benchmark h1 but sounds i can live with it.
i think that more impedance = more resistance = harder for the harmonics.
the best is let your ears decide whats best for you, in a super store.
i like color sound.
also try moddifications, like changing the headphone cable, with belden or gepco, or canare or mogami,.