For my tastes, HD800s sound way too bright and weightless in terms of bottom end, it's the poster-child of the "more treble tilt = more balanced" trend started by German headphone companies 10 years ago. In terms of technicalities it is a marvel, but that is pointless to my enjoyment when the sound signature and voicing is so off.
Man, you are really asking for it from those guys. Well honestly I have never heard the hd800s but from reviews I had gathered that the treble was a little too bright. However, from reading only, I see that they have an excellent soundstage. For 1k though I think I would wish for some better sound. I really like the sound signature from my hd650s, but the hd800s are supposed to stray from that. Still cannot part with he400s or the hd650s even though i find them somewhat comparable. They have just enough uniquness that I can still appreciate them seperately.