I listen to pretty much anything. As for deciding on a headphone for a genre? I don't usually do that, If I could I would just use one perfectly realistic detailed headphone. I think they are both great headphones for all of those genres. If I could I would merge their best qualities together, the k7xx deeper more linear bass, and treble, combined with the very consistent frequency response and slightly warmer sound and smooth vocals of the hd650.
If I had to choose between the two? it would probably be the hd650 just based on its smoothness and consistency. It has no major variations in its response. The k7xx on the other hand has some dips and peaks: a peak at around 2000hz, a dip around 3000hz, then another peak... It was the inconsistency that ended up deciding it for me. I think it is part of how it gives the impression of such a large sound field. To me it just made certain vocals sound a little more harsh, and the treble a little rough.
The peaks and valleys aren't even that steep or that noticable, and the overall effect is still a very linear realistic headphone. Also my ears are apparently sensitive to 2000hz, so that relatively small peak ended up really annoying me.
But thats just a personal preference, plenty of people say the hd650 sounds boring, or not lively enough. I just think it sounds consistent, though once again, I wish it had better extension to the extremes, but at least that is easy to add back in EQ if i needed to. Also the headband system of the k7xx was really loose on my head, and slides around alot, I prefer the comfort and clamping force on the hd650.
I guess I would just ask which qualities of the k7xx are you dissatisfied with? If there isn't anything you can think of or are fixated on, the k7xx is really good.
Also, at the $300 and above mark for headphones diminishing returns on audio quality kicks in much harder (I consider both of these headphones in the $300-400 range as far as quality goes). So whether it would sound substantially better in those genres to you, would be based substantially on personal tonal preference. Every improvement in sound quality is fractional after this point.
My pick of the two is the HD650. They are both very linear and realistic headphones, but I prefer the overall presentation from the HD650. Sorry I'm long winded.