I had DT880 pro-250 verison and I didn't like them and I had the headband bent and they doesn't sound the same to me as the DT880 premium 600's. But then when I had the DT880 pro-250s I had used them with both a E9 and a STX that I had during the time of owning them before going to a A900X.
And that's exactly the kind of testimonial that gives the 600 ohm version its rep - mostly people who heard them at different times, often with different amps. Like this fellow who later did a more controlled comparison and concluded no difference: http://www.head-fi.org/t/506963/dt880-600ohm-bs/60#post_6868111
And of those who claim to have compared them in person, they seem to just as often prefer the 250 ohm variety as the other way around:
Still others say exactly the same:
They have the same drivers.
Edited by Kon Peki - 3/10/14 at 7:10pm