Just my thoughts. The Signature Pro and Signature DJ has more resolution than the 3 aforementioned above. Personally I feel that the Ultrasone Sig range are just simply the next level up. And if you're looking at getting more detail and resolution, then you'll just have to splash the dough now to get to that next level. And even that to me is climbing the ladder "slowly" (otherwise I'd say go straight for the Fostex TH-900 ;-)).
At least in my thoughts, although I'd personally rate the TH-900s the top of the closed back range, they're non-isolating which makes going out with them a no-no. Therefore my next level would be the SigPro (if it's one that passes good QC) or SigDJ as the top isolating closed backs.
Time to move up buddy.
Pretty happy with my Sig Pros and Mad Dogs... I would LOVE to try the Sig Djs and the TH-900s! But I guess I'll wait for the TH-600s (and differences between them) and the Audeze closed-back...