Thanks for reading and for the comment!
I think the Custom One Pro is a totally decent choice for metal, as is the DT770. I’d probably slightly lean toward the 770’s, if you don’t mind the attached cable. Their bass response is perfect and their speed is great for guitars.
I actually found the DT770s originally because of metal571’s praise for them, and if you couldn’t tell from his name, he’s a pretty big metalhead.
For open headphones, you’re going to lose a lot of bass response, and that’s going to make a lot of rock music less exciting. I’ve enjoyed the DT990’s okay, and I’ve heard good things about the Fidelio X2…but personally, I think rock music sounds better on closed headphones.
Hope that helps you out in some way! I know it can be daunting, so make sure the place you buy from has a good return policy and that way you can feel a little easier about it.