I've actually bought both. Here's my opinion: the Glacier has more forward vocals, while the MK III is a bit warmer and the vocals are less upfront. The treble on the Glacier is smoother and, in my opinion, better. You can hear the difference when you compare them side by side.
Oh, and one more thing—the Glacier is comfy but heavier than the MK III.
Could you please tell me on the Dunu Glacier if the 's' and 'sh' sounds are harsh and very prominent due to the 6k peak on the graph? Is it aggressive, can I listen to it at loud volumes without it being harsh on the upper midrange?