Ended up getting the X1s, after a week of listening I'm quite happy with them. To my untrained ears there isn't a resolute difference between these and my M50s in terms of sound quality, but the open design does give it a nicer feel. The comfort is also quite fantastic, with the M50s I always felt like they were clamping my head and had to take them off after a few hours due to fatigue, though the area of irritation was generally the top and sides of my head and not the ears as they fit snuggly in the cups. The separated support band on the X1s seems to have alleviated any sense of fatigue, I found myself even forgetting I was wearing them at times, and the nice foam/velour pads aren't clingy like the pleather pads of the M50 (which I finally replaced with velour pads only last month).
I'm thinking I'll keep the M50s rather than selling or giving them away, they still sound good to me and I think it'll be nice to have cans that I don't necessarily have to baby. They lasted well over three years and are still in good condition, and are also more portable due to the folding design.
An issue I noticed with the velour pads of the X1 is that what I assume is the dye used on them wears off, not on my skin but on the surface of the table I laid them down on. I thoroughly cleaned the table surface and didn't observe any change in behavior, so I looked into getting a headphone stand. I didn't like anything I found in the price range I was willing to spend, but last night I realized my fan seems to do the job very well. Will probably stick with this until I design and build my own.
