I'll throw my 2 cents in too. I agree with Oderi, the Mad Dogs might be worth putting on your short list. I havent heard the Mad Dogs per se, but based on how my modded T50 sounds I'm sure it sounds awesome. I responded to an Oderi post in another thread with regard to looking forward to his impressions of the Mad Dogs versus his d5k's. I had the d2k's a while back and returned them to headroom. In a word I thought they were boring, YMMV. I actually preferred my SR60's to the d2000, but I'm not a bass head per se, and I preferred the forward mids of the SR60 to the slightly recessed mids of the d2k. Also I listen to a lot of bluesy guitar driven rock, and again the d2k's were just meh sounding IMO, too laid back, lacked the attack of a Grado. I'd love to hear that he400, I've been hearing a lot of great things. Lot's of Grado heads switching to ortho's. I know for me the curent incarnation of my T50 is fuller, warmer, and lusher than my hf2. I'd go with the he400 personally, but that's only because I already have a modded T50, wasnt to fond of the d2k, and never had any interest in the 650.
Honestly the HE-400 is just a fantastic sounding head phone. I prefer it to my HE-500s for most music. It does not have the best bass, the best mids or the best sound stage i have ever heard, but it does everything very well.