i can not know what you're thinking unless you write it down. just because you picked a few similar styles of headphones does not mean any of them are the best for your needs.
the m40x is worse than the m50x.
the m50x and mdrv6 are easy to drive but have horribly small soundstages which arent good for gaming. the v6 is "brighter" while the m50 is "bassier".
the hd380 requires a good amplifier to sound okay but reproduction of some sounds is "off"
if you need closed yet need good soundstage for gaming take a look at the dt770. you would want a portable amplifier for it but it would be a better choice.
i own an m50 and do like its sound, but i'm being honest about its very small soundstage. for music that isnt quite as important (which...