I've made some more observations pertaining to HE-500 vs. HD800 in rock/pop genres. I've found the larger soundstage and detailing not to be so important in these two genres. These are not large soundstaged genres to being with, and as for details, there's a lot less subtleties compared to other genres. The biggest thing I found the HD800 to have over the HE-500 for these two genres are the vocals. I found the vocals to be smoother, more forward, and encompassing. And obviously the biggest thing the HE-500 has over the HD800 in these genres is the bass impact. I guess I would recommend the HD800 for lighter, softer rock and pop, and the HE-500 for harder rock and bass centric songs.
Again, these are very chain dependent observations. See my sig for my chains. In another thread I went more into detail on my chain, various pairings, and some interesting finds, such as how I believe the Quickie to pull a lot weight in my HD800 chain, especially for it to sound euphonic to me, and put it on par with the HE-500 for rock/pop.
http://www.head-fi.org/t/607079/beyerdynamic-t90-d/1395#post_10124880