i posted a couple pages back about it, i can't remember myself which page. basically hd650 was perfect for me for my inner ear condition. but it was way too thick for my taste.
i couldn't stand the lower midrange thickness of the hd650 when it paired to anything other than OTL amp. That was after 6 hours audition on and off.
i find that i'm more of a hd600 guy myself, the short 5-10 minutes i auditioned them (different store). Where i'm at, locally, the distributor is asking for $560 for hd600 and $620 for hd650. I can eat the hd650 price, $500 to $620, but i dislike the $400 to $560 hd600 jump, especially considering $300 deals popping up all over the internet.
So i might as well get the he-400i for $640. That's basically the primary logic. Secondly, a head-fi member told me that he400i is not as bright as hd600, Well, nice.
Third, since i own this headphone called sony ma-900, a $400 hd600 would be nice, but a $560 hd600 is redundant and too expensive.
so tl;dr 1) i won't buy hd650 2) i don't feel like paying that much for hd600 3) get the he-400i instead.