also because i like the idea of improving
Again, this is science talk. You are trying to place a matter of personal opinion into a hard line fact.
Yes, many people prefer open back. Many people might rate the 58x above the M50x. But at the end of the day it's a matter of opinion, not fact. You can think of it as two different dishes that have the same price tag from two different restaurants. Maybe one is using fresh noodles made daily while the other is using all organic ingredients from the sauce. One might even be rated higher than the other from all the local blogs and press. But at the end of the day, that doesn't mean YOU are going to like it. And YOU will not know until you taste it.
But again, not life or death. You try it, and if you like both, you can have both as your daily tastes suit you. If you don't like one enough, you can sell it. Sometimes you might really want to try something from a fancy restaurant but you simply can't afford it. So maybe you save up for a special occasion. Maybe a friend goes and lets you enjoy some leftovers (used gear). Maybe you go, and you hate the food and feel it's wildly overrated. That's just part of it. And it's part of audio. Sometime you bite the bullet and it doesn't work out. Sometimes the reviews align perfectly with your taste and you have a new favorite dish. BUT it will never be a science.
The same general rules apply though.
Usually, if you spend a lot more, things tend to taste better or be a more refined experience. Not always. Sometimes it feels like a waste and you don't click with it or you don't get the hype. But if you're looking at two dishes of the same price from the different restaurants, it's likely that you will prefer one, but that doesn't make it factually superior to anyone but you.
Also, at the end of the day we're talking about $150. Yes, I understand that is a notable amount of money. But we're also talking about it on a record forum. A "vinyl diet" as (
@Lee Newman would say) can get you there fairly quickly. Not to mention the 58x and M50x both regularly sell for $80-100 used. You can always sell one to fund the other. Even if you get the 58x, hate it, and sell it, paying $50ish for an in home demo really isn't a terrible price to essential rent a nice set of headphones for a certain amount of time.
I'm going to toss out one more thing you probably won't like hearing. If you're profile is accurate, you are 20 years old.
This is a hard fact of reality. I did not purchase any audio equipment expect one Bluetooth speaker and throwaway ear buds from the age of 18 - about 26 or 27... because I just couldn't afford it. I was able to buy more audio stuff while in highshcool under my parents roof than I was in my early and mid 20s. Once I got a house (at 31) I finally started really getting back into audio. I wouldn't have dreamed of $150 headphones with dedicated amps when I was in my early 20s. I had more important things to finance, like school and rent. At the end of the day, this hobby is expensive. My BT speaker was considered a major audio purchase for me at that time, and it wasn't even hifi. And I waited until post-college to buy that. It just gave me music on the go. Sometimes that's reality. It's not bad, but it does require focus and patience.