And considering you are open minded about the closed back, have you heard or know much on the K171? I like their physical design the best, but I question whether they would have the sound stage or the clarity that the K612 might. Also they come with some amenities, like detachable cord and etc.
Well I do find the majority of open-backs to sound better. It's really hard to find a truly good closed back. The K171 won't have the soundstage, clarity, detail, refinement, naturalness of sound, etc. when compared to the K612. The K612 is going to be the better headphone by a large margin without a doubt. I do wish the K612 came with a detachable cord but ended up not being that big of a deal for me at least.