Just got my GR07 Mk2s today.
I've compared them straight out of the box (without any burn-in) with my Miracles and they stack up really well.
Very similar signature and presentation. As you'd expect, the Miracles are better in basically every area, but they really are like a GR07 on steroids rather than a vastly different earphone. In other words, if you like GR07, you'd probably like the Miracles.
Initial impressions are that the Miracles are more open in staging and detail retrieval is superior. The GR07s may improve in both areas with burn-in, but I don't expect them to catch up.
What's impressively similar is the balance of the sound. Both earphones cover the full frequency range really well without any obvious emphasis. More listening may reveal some differences, but early impressions are really good!
One plus for the GR07s is the fact that they're 50 ohm earphones and will run really nicely from a lot of different sources. For instance, the GR07s actually sound smoother running straight from my AudioQuest DragonFly DAC whereas the 16 ohm Miracles are a little rough from the DragonFly and really benefit from the control (not power/volume) of an amplifier (Tralucent T1 in this case).
All-in-all I'm really impressed with the GR07s and can't wait to hear them after burn-in.
How long do you recommend before they reach their optimum sound?