Even though I love the DT-150, I think you'll find some overlap with what you already have. I would suggest getting something in the $500-700 range for a step up like the HE-560 or the DT1990 Pro if you want to try Beyers. The DT-150 are a great value in their price range, but I think you already have some good value cans in that general range $200-400.
From my own experience, however, I can only say with 100% certainty that the DT150 are better than the Momentums. I also like them better than the HD650, but at times they are not 'better' per se, but just different. They have a lot of bass, good mids for vocals, and a sparkly clear high end. Yet they have some dips in the upper highs that helps make things sound smoother and a tiny bit darker than they should. They are also surprisingly open and wide for closed headphones. BUT, you are not going to get the value out of them today that they were 3-4 years ago, before a lot of others came into compete in in this price range. In my opinion if you don't have any closed headphones in the $200-400 range, these are great for acoustic music with a good source. But if you already have that, you should probably look for something different. Both the X2 and the Maze 99 Classic are competitors to the DT150, and I think some will prefer one or the other, but they are probably all three in the same league (except that the DT150 is by far the ugliest of the three, if you care about that).