Why not just wait for the M-100s to come out, where you can get the best of both worlds? That's what I'm doing, anyways.
I'd advise against the PRO700mk2 unless you are willing to go an extra mile to make them better. They can be incredibly uncomfortable unless you put cotton under the pads. However, if you mod them correctly, they are comfy, attractive, portable, ludicrously bassy, and so durable you could run them over with a bus and they would be undamaged.
Are the M-100s gonna have more bass than the 80s?
From what i have heard the M-80s might not have the bass i desire??