Between those 2 for music production M50 would be the clear choice, PRO700MK2 is too colored. However if you want an alternative take a look also at http://www.m-audio.com/products/en_us/StudiophileQ40.html because I have a hard time to find anything that M50 would do better at than these, I think it's slightly better compared to M50 in every aspect, the bass is punchier, tighter, snappier, more textured and mids and highs sound more neutral and balanced. Dubstep is just awesome on these, it made me realize even dubstep can have more than one-note bass haha. It's anything but muddy but it's also not too bright or harsh, so therefore I'd call it neutral but with a bass boost but due to how well it handles bass it doesn't seem overly bassy at all. However I'd recommend some basic amping though to get the full potential out of them as then they get more dynamic and bass gets alive.
Forget the Crossfade LPs.
Thanks! I guess that helps me with my choices. I still like the design of the M50's and I have never had a high-end pair of headphones either. This would be my first and I don't have enough for an amp really