Super delicate, I should say.
Plus self unscrewing cups (wasn't it you who lost cups on TH900 twice), flimsy, barely padded headband and twisty cable, all were sure signs for me that this thing won't last. I've owned D2K and D5K. They could have good drivers (if they fixed farty Fostex Denons bass) but enclosure is underdesigned.
T5P just look like phones worth their street price, plus I have T1 and like them (comfort, build and sound).
Signature DJ, I don't know, too plain and ... white? Same design as HFI, which is rugged no doubt but wasn't the most comfortable for me, and cheap plastic enclosure is definitely not up to asking price. Sony MDR-7520 for instance at third the price just ooze "premium" all over.
I know, you can say that sound is all that matter, afraid when it comes to phones it's not that simple.
I've always had that "fear" of rocking out with the D5000s and having one cup fall! :p
And I agree actually on the design and looks of the Sig DJs. They DON'T look like they are worth $1k but they do feel like it ;-). Regarding sound, it's all diminishing returns up to a certain point so who knows, besides the bass, maybe the MDR-7520s you'd prefer in all aspects over the Sig DJs.