The only two Beyerdynamic I have heard to this day are T1 and DT1350 and only briefly. Sorry.
The UE900 I am not a huge fan of, prefer the 4.Ai a lot more for the same price. That being said, at half price, it does sound good. This is subjective of course other opinions differ.
Now what I have heard so far are a lot cheaper than the ue900. The single and twin BA although great value, don't live up to the UE900 although the twin is getting there, and does have positives over. The HY3XB I have does not compare apart from in bass a quantity an sub bass texture in which it destroys!
Now for me to compare to the BA3/4 or any other models as guess work would be wrong. I am loving the BA models from Cosmic and they certainly know what they are doing but I am not going to try and make a guess. I will keep you posted on my journey through cosmic none the less and help you out as much as possible.