My first Ultrasone was the 700 and my second was the 780. Of those, I use my 780, since I took apart my 700 and did stuff with it. Both the 700 and 780 sound very similar. I did not listen to them back-to-back, so they could even sound indistinguishable for all I know.
My roommate fell in love with my 780, so he wanted to get a pair of Ultrasones. I suggested he get the 580 because it is the cheapest in the HFI line, so I knew it would sound similar. I've listened to his 580 and must say that is sounds very good to me. The only difference I can think of between his 580 and my 780 is that I got the impression that the 580 had more bass, but I could be imagining that; I listened to his music, not my own.
If you enjoyed the 580, you will enjoy the 700 or 780 equally. Get whichever is cheapest.