Suprisingly though, my T70p fares much better than loaner T1 and my older DT1350. Relatively better than any of the IEMs too. The most problematic is the 5-6k hotness (not ringing apparently, or relatively low), as it causes the soundstage to flatten and warp, not unlike old GR07, but without (or with much less of) the ringing which caused sibilance with it.
Also, it could use 10 dB more adjustment for the highest end > 17kHz. It's there all the way up, but is very quiet.

Unfortunately, I was unable to find a closer match in terms of signature than these that's also technically proficient.

I probably should send them in for measurement some day. The tricky part is that overseas shipping is pain and expensive. First, I might ship DT1350 first to see what was the baseline performance for comparison purposes.

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I agree, these sound reasonably close to DT880-250 which I've auditioned side by side. However, 880s had even stronger 5-7k boost, but were a bit smoother and had notably recessed mids. They also sounded far... harsher or colder I think. Distortion?