TH-900 definitely. It's completely different from a HD650.
The D7100, even though I am one of the few who seem to somewhat like it, is nowhere near the quality of a TH-900 and and has nothing in common as well. The TH-900 is an improved D7000 but has no relationship to the D7100.
Concerning planars, I'm not a fan, imo it's an aquired taste. I used to have an LCD-2 for a while and it was about the worst thing I ever heard, so bad I decided to avoid planars in general. The new TH-500RP does peek my interest though but I see the opinions here on HF are generally negative.
Regarding the TH-900s treble: I never heard anything but smooth, natural highs, never had any harshness with any kind of music or any amp I tried it with, even the simple output of an integrated amp.
It is somehing I used to associate with the HD800 so what I read in the last few posts here is about the opposite of my experience and I have two pairs of TH-900 that are about 1500 apart in serial numbers.