First of all, kudos and a big "Thank YOU!" to David for dedicating so much time to this comprehensive guide. I believe he deserves a canvas Time Bandits/LOTR style map of the "Kingdom of Headphonia" for all of his hard work.
I've heard nearly everything (IEM's excepted) on his list short of a few outliers such as the Ultrasone and JVC, and generally agree with his rankings from the Orpheus on down. I've long held the HD600 and Grado SR-225 as price/performance leaders. However, my one significant divergence is with the HiFiMan HE-500... it just doesn't fit into the way I view the headphone hierarchy.
I briefly owned the HE-500 and paired it with a Decware Taboo. The HE-500 delivered satisfyingly deep bass and excelled with certain instruments such as the piano. What bothered me most was the uneven soundstaging. Human voices sounded as if they were coming from a different area of the venue, as if artificially recessed or encased within a plastic bubble. This lack of cohesiveness across the band was frustrating to experience. My mind wanted to enjoy the excellent rendering of individual sounds but was unable to integrate them uniformly. By comparison, my Grado 225's (despite being less sophisticated and having a smaller soundstage) were much more fun to listen to via the Taboo because the sound was consistent across the spectrum.
I didn't keep the HE-500's very long. I found them to be rather heavy, hot, and required occasional adjustment to prevent the hard surfaces of the speaker area from brushing against the top of my ears. Overall refinement & appearance was a bit rough in comparison with other peers at this price point. I dunno... the HD800 in my opinion vastly outclasses it in terms of detail retrieval, neutrality, comfort, soundstaging, fit and finish, and realism. Like, no contest.
*shrug* I'll have to confirm this at the next Head-Fi meet & contrast with some LCD's to find out what's what.