Yeah the m50s have a smaller sound stage than those two. The 598s have the better sound stage compared to the X1s in my opinion. They're also known for their mids (something I didn't know I loved so much until I got them). The sound leakage is pretty substantial. Imagine setting a pair of normal closed back headphones down and playing them loudly. That's about the amount of sound leakage that you get from open backs when playing them at a normal volume on your head. For instance if I'm on Vent/Skype with friends, they can hear what music I'm playing when I turn on my mic. You can hear about 95% of things going on around you, they're very open. I like this feature, but I know many don't.
I love the mids on the 598s. I listen to a lot of metal/rock and I think they really shine there. Their sound stage and instrument separation is so much better than the x1s in my opinion. It's hard to describe but you can separate the different parts of the song better in your head. They're also more detailed to my ears without sounding harsh. And something else I didn't know I valued so much was comfort, they're very light, they don't get hot and sticky, and the don't actually touch your ear, they sit around it. I'll forget I'm even wearing them at times.
However, they definitely are not a bass can. Some even complain that they are bass light, though I never found that to be the case, seemed closer to flat to me. Over about a week I stopped noticing it, and now when I hear a bass from the m50 or x1 it seems overpowering.
Just a heads up, last year near black friday Amazon had a deal on the 598s for $100. If you're not in a hurry it might be worth waiting to see if it happens again.
Nope not a bother at all, glad I have all three to help!