The M50s imo would be a poor choice. They're meant for bass. Not for gaming. Open back headphones generally give you better gaming because of their sound stage. You'll be able to hear enemies footsteps around you etc.
Open backs have shown me just how poop they can be for gaming. They don't feel one bit immerse at all to the whole gaming experience. Slightly open, or "ported", headphones are alright. But open backs like the HD555s are just garbage.