Blergh.
Ordered the Sennheiser HD 280s. Underwhelmed. The sound isolation is, at best, maybe a little better than my Sony MDR-7506s--although the difference is close to imperceptible. The Sennheiser audio reproduction is definitely not on par with Sony; the Sennheisers do have "crisp highs" and "punchy lows" (which is apaprently all consumers care about these days) but the midrange sounds "honky" and artifical whereas the Sony performance is smooth and perfectly natural.
At the end of this whole endeavor, the Sony MDR-7506s perform at least as well at "sound isolation" as any of the "sound isolation" headphones I've tried, and they sound much better. The Sony MDR-7506s are the exact same model of headphones I used 20 years ago.
I found this site, which posts detailed specs in their reviews:
Sony MDR-7506
Sennheiser HD 280 Pro