I would argue that the P5 doesn't keep up with the rest of the list.
I would abstain from any comment on the Mad Dog as I haven't heard it, but would pay attention to comments from others about amping... that stuff is important
You don't mention source, and to repeat, that is an important factor.
Of those left on your list at this point, they are such different styles and design that I would not follow any particular opinion, regardless of how well qualified, as to which sounds better than the other. In fact, I would be suspicious of anyone that does not call out the fact that the K550, Momentum, M-100, and P7 are all very much subject to physical fit/feel between users and different sonic signature between a variety of ears as to mandate, more so than ever, that the choice between any of them are personal and nothing else and no one else matters.
Yes, you can confidently say the same about any two or more headphone models, but these in particular just scream for that foot note in any evaluation.
I don't know about the HP50, but if you dig the style at all it is clearly worth a close look and I would not be shocked at all if it outperformed all the below on your head, according to your ears/brain. When I get a chance to hear them I may land in the same place, but I just don't find the style/design inspiring so I know I will invest in some different choices for the foreseeable future...
Having said the above, here are my own conclusions after some listening:
P7 - in store demo, didn't feel right but had very good sound...better than Momentum to my ears in terms of balance and resolution
Momentum - does not work on my head at all, had to pass, but did think it had a very pleasant sound
K550 - owned for a year, loved em, except the highs become strident at moderate to high listening levels after a while and sometimes the mids come off a bit strange. great fit and bass response, but many others have felt otherwise in this area.
M100 - just ever so slightly behind the articulation/resolution of the P7, and the space and mids (when they flow) of the K550, but feel great and I think the bass translates beyond rap and EDM, I think it works very well for rock and I love the design and build quality, so I have a pair arriving any day now... Never liked them a year ago, but as my listening and fit experiences have evolved over the last few years I have grown to appreciate them and vote with my hard earned cash. I initially never liked the strong bass, but now I know it works for a bunch of music I like and for low level listening at the office or blasting away at home, I expect it will never be my "go to reference", but I predict I will use them and love them for a few years before I get bored and try to move on, if ever. I am hoping they stay in my "top ten" for a while as I add to my collection (another few years before I own 10 headphones). I am biased by the fact that they will also serve a portable role for me without being small or fragile, as I admire the folding joints and case, so that scores some points with me
If at all possible, you must get these things on your head to make a good decision... so if that is not possible, plan to buy/return until you know you have the right one. Good luck.
Edited by Greggo - 12/6/13 at 1:35pm