[3nity]

   I am also using my HD800 for mastering purposes, they are accurate and flat, especially below 1k, and many studio mastering houses use them.

Late to the party, however I must agree with you: the HD800, imho, are the ones that translate well in critical mixing/mastering sessions.
IME they are perfectly driven for this task by the QES Labs HPBA-2 balanced amp. This combo is hyper analytical, retains the last bit of micro detail,
lightning fast responding on transients, absence of colouration, ruler flat frequency and phase response. Exactly what you need when referencing a mix.
YMMV of course.