I wrote, and re-wrote, and changed pads, and bent the headband, and un-bent the headband, and here’s my review, finally.
Fostex T50RP MK3 Review (with Shure 840 pads): Hard hitting, cold precision.
First: Way too much treble, stock. Shure 840 pads are mandatory if you want to hear bass/drum kicks, etc.
They’re my first planars. What are planars? With planars, let’s say the music hits, hard. And fast. And stops fast too. And not only the bass hits. Everything hits. The snares, the cymbals, etc. You know, when you listen to, let’s say, an uplifting 140bpm trance song, and then after a bit of silence, there’s the kick and you go “oof!” Well, prepare to clearly hear the silence (yes), and then go “oof” 140 times per minute with T50RPs. Lol. Fun stuff for cranks, haha. If you wanted to sit back and relax with scotch on the rocks and T50RPs, nope: You will be dancing on the carpet after 2 minutes. If you press play, that’s because you want to feel all the energy that was in the studio. And they’re really analytic. So smooth jazz will be as relaxing as being there… lying right next to the drummer and the saxophonist. Because planars are relentless, and T50RPs can be really, really dynamic.
-Bass (again, with Shure 840 pads): I’ve never heard this much precise, strong and accurate bass and sub-bass. I already talked about the kicks/drum kicks, too. Skull shaking stuff. I even got nausea one evening after listening to electronic music at high volume. Just once, but still. I’ve listened to electronic music with HD280 Pros (they allegedly go to down to 7hz) for years, and never experienced this. Some people have the same problem with subwoofers, apparently. Well, it makes sense. T50RPs planar technology hits hard, and goes low. I mean, you can even hear the bass in Metallica - And Justice for All! 
-Mids: They’re neutral, but they seem a bit V-shaped. That’s because the “high-mids” are all there, but… not often. Maybe T50RPs are just “too dynamic” : There’s obviously no drum kicks, bass, snares or cymbals in the high-mids. But with violin strings, or when a girl screams, it’s glorious (uh, yeah, I’m still talking about music, guys…).
-Highs: They don’t extend all the way up to 20khz, but, huh, there’s not much there to hear, obviously. They sound really clear, because they have treble but lack “high-mids”. So, what the hell are “high-mids”, you say? Well, I’ll be more precise, I found a graph at Changstar: Just look at this hole from 2khz to 5khz (see below) compared to HD600s. I don’t have HD600s, but everytime I try to convince myself T50RPs are neutral all the way, I plug my HD58Xs and realize there’s something missing. This lack of “high-mids” can make 'em sound thin, or “cold”, especially combined with the precision of planar technology.
Oh, and ignore the -5dB @ 20hz: It’s definitely fixed with Shure 840 pads.
The precision of planar technology.
I probably shouldn’t confound “thinness” and “precision”, but I’ll say that anyway: these planars can sound “thin”. T50RPs are the exact opposite of my HD58Xs, in which everything sounds “fuller” and “warmer”. And with overdubbed, compressed songs destroyed by the “loudness war”, they can even sound like you’re listening to exploded speakers. Yup, that’s what compression sounds like. And, in my opinion, that’s all what T50RPs are meant to be. It’s just “the price to pay” for precision. As I already said here, I got 5/6 on this test (.mp3 320kbs vs .wav files). Everything is there. Everything is detailed. Everything jumps at you. You just don’t hear “reverb” or “soundstage” when there isn’t.
So, no graph could have predicted that, not even CSD graphs, but I now have two “complementary” but neutral(-ish), studio-ready headphones. Between T50RPs and HD58X, I was just expecting “more of the same”. Boy I was wrong. I really can hear this planar technology. I’m really lucky!
And now, with a smartphone:
“Too dynamic” doesn’t sound fun for some, but I only said they can be “too dynamic”. Yup, T50RPs can sound thin, even mechanical… Try giving these LESS power (!). With lower power, like with a smartphone, T50RPs suddenly become smooth, low-volume critical listening beasts! Detailed, analytical. Way less dynamics, exchanged for way more detail. Behold T50RP, the Japanese mech engineered to devastate all your bad studio mixes… with your damn smartphone.
I don’t have a 1 watt yeet cannon (copyright Zeos), so I don’t know if they’d be the same with a lot of power. All I know is, my jaw dropped when I heard a ton of unheard details and hiss, with what most – well, especially Zeos, would call “not enough” power.
P.S.: No “planar crinkle” even with beard and long hair. I still don’t know what “planar crinkle” is (they’re a tiny bit “open-back”, though, and I heard it was something about pressure – not a problem here).