Thank you for the Crinacle link on the MSR7B, TSelanne. Crinacle appears to have added quite a few new headphones to his graphing tool since my last visit there!
https://crinacle.com/graphs/headphones/graphtool/
Since I just got my DT-770 and M50X a few months ago btw, I'm not really lookin for another closed-back at this point. Unless I run across something in my price range that looks like a much better match to my preferred sound signature than what I've already got. And also as comfortable and reliable as the DT-770 has been so far. The Crinacle plots on the AT MSR7b don't look too shabby. But they don't appear to be a significant improvement on the AT M50x, and 250 ohm DT-770, in terms of their tonal balance. And maybe a step back in some ways from the kind of thing I'm lookin for. (See my notes below though re the L/R bal. on all these HPs.)
It's helpful to see some new and different plots on my current headphones though. I don't think Crinacle had plots of both the 80 & 250 ohm DT-770 the last time checked. (To view the 250 ohm, click on the down arrow (v) after the name of the headphone in the title bar that's below the graph on the right side, and select it from the list.) They appear to confirm a couple of my suspicions about the differences in tonality between the two though. For starters, the 250 ohm DT-770 has more sub-bass than the 80 ohm. I could definitely hear that in my comparisons, when listening to them on the same amp. And the 250 ohm also appears to have a bit more air in the higher frequencies. And I believe it was the combination of those two things which lead me to perceive that the 80 ohm version as being a bit more "mid-centered". The notch at 4 kHz also looks more pronounced on the 80 ohm version of the DT-770. And I believe that is something I also noticed. Though it was probably less obvious than the differences in the sub-bass and treble.
The plot of the 250 ohm DT-770 also appears to shown an imbalance between the right and left channels, which favors the right channel by a dB or so. Which is also consistent with my experience. So it looks like that issue could indeed be in my headphones rather than some other gear. And it looks like I'm making the right type of correction to compensate for that. The plot also shows that the imbalance is pretty consistent across most of the frequency spectrum, rather than isolated only to certain spots. Which is also useful to know. Because that means I don't really need an EQ to fix it. And the simple L/R balance adjustment I've been using is probably sufficient.
The drivers on Crinacle's 80 ohm DT-770 plot look a little better balanced though. And like they might actually be favoring the left channel a bit in the bass and mid-treble, which is interesting. I did not listen to the 80-ohm DT-770, when I had one, as much as the 250 ohm. Because I took a pretty quick shine to the latter. And was really more interested in a higher impedance HP.
The L/R balance appears to be very good on the AT MSR7b btw. Particularly in the bass and midrange. But less good on my AT M50x.

...Oh well. You get what you pay for, I guess.

The imbalances don't look quite as problematic on the Rtings M50x compensated plot...
https://www.rtings.com/headphones/1-4/graph#295/3992
I'm fairly sure I could hear some differences in both the bass and treble though on my pair. Perhaps that's somethin that could improve a little after some break-in though.