In contrast tonight I could hear that there was a difference between the Mojo and GOV2 immediately, and in terms of specifics the bass difference came through pretty rapidly. With the GOV2 the bass was more weighty and impactful, the sound overall more dynamic, which made it a better pairing for the Ether C than the Mojo to my ears. Cymbals sounded a little more splashy with the GOV2 however, and I would imagine over a longer listening session it could be a bit more fatiguing (although I may be overestimating that, given I am a bit more sensitive to sound with the nearly resolved cold). Interestingly if I changed the digital filter on the GOV2 to the FRM filter it was less fatiguing, cymbals were a little better behaved, and it sounded closer to the Mojo signature, while still retaining some advantages in bass and dynamics. Soundstage and detail retrieval seemed similar to me, and it would take more sessions to meaningfully flesh out if I could hear any differences in those (or other) areas.
I am unfamiliar with the Beyer headphone, and have no desire to renew a relationship with their cans - I am familiar with the Ether and Ether C, and loved what I heard. The above quoted paragraph, I share your view completely.