Hey Greggo. I know you didn't ask but I would seriously reconsider the HD700 as your end game. The HD700 has been pretty much a failure. I hear even Sennheiser thinks so (according to Sennheiser "insiders"). Why you might ask? It has an insane treble spike of death at 7k and the resonance will leave your ears bleeding. I would just get a used HD800 or a refurbished one. A used HE-500 or HE-6 won't be bad either. Just putting that out there so you do more research. The HD650s are golden for the price of course and also the HD600.
As for the Concero I think it beats the Bifrost (non-uber) quite handily. Not really even a question, but just dominance by the Concero in every way possible.