Here's the set of measurements for CEE TEE's HD800.
Maybe my ears are tinned, or his rig is just that good at rolling things, but 6KHz and above don't bother me as much as many other headphones, or the stock HD800. I hear a "peak", but it dies off pretty fast.
Note: CSD shows -35dB floor relative to all other freqs, but that's practically -45dB for >6KHz, and that's... super amazing. I tried going to -50dB for every other freqs (which means -60dB for >6KHz) and still no ringing. In actual listening, there was no ringing either. I heard a peak that died fast, and that was it. Resolution is superb, and soundstage is retained.
Good job, CT! This one amazed me. It actually sounded just ever so slightly brighter than my reference.
P/S: slight channel imbalance (left channel is 1dB higher than right?) is not heard as such per se due to massive soundstage. I couldn't hear it. And CT's preference is about 2-3dB slanted to the left so I'd say that's almost perfect for him.