I personally cannot stand the HD650. I bought a set a little while back and was pretty excited because people rave about them, but all I was hearing was MUSH! So much low-mid bass, it was thick and just unpleasing. I had owned the HD580 and HD600 before that so I thought it would be similar to those at least a little, but it was all just muddy to my ears. The treble clarity was OK, the bass was decent, but I was totally distracted by the mid-bass hump.
Sold those and bought an HD700. The HD700 is like an open-back Z7 sound-wise. I could sell the Z7 and get an HD700 and have about the same signature with a slightly wider sound stage, but the Z7 is too damn sexy.
Now, Z7 still has that powerful mid-bass, but somehow it is just so dang pleasing. I think the Z7 while having "bass", it is fairly balanced within the bass-frequencies spectrum. It is kind of funny, some people dis-like Z7 "bass", some people find it "not-enough". What funnier is that Z7 bass varies a lot through different sources. For instance, it bass is thicker and boomer with Zx2, with TRRS out on Zx2 it is faster, still thick, but toned deeper, with my receiver when I watch movies it is tighter (not faster) and not as deep....with V10 smartphone it is tighter, deeper, faster, and less boomy....etc. I prefer using it straight out of Zx2, so I made changes to it. Now it is just magical with zx2 and TRRS. I had tastefully mod it (invasive processes) into satisfying trebles range with wet, and fluid, detailed bass. I love it.