I think it's hard to say, since M50s are closed-back, while the HD595 are open-air. eric0531 pegged it with his last comment, "...if the house is quiet...", in my opinion. It's hard to use open-air when the surrounding area is loud without getting outside interference. My preferences, when it comes to music, are that open-air headphones generally beat closed-back headphones in the same price-range when it comes to accuracy and neutralness.
The only exception when the M50s excel against the HD595, in my opinion, is perhaps electronic music or rap and hip-hop with exaggerated beats. Even then, some people prefer a cleaner, more accurate bass than heavy, boomy bass. I personally like the bass coming from M50 and similar closed-back headphones when it comes to those two genre, but that's just me.