I have both the MK II and BE and even though I'm not the audiophile a lot of folks here are, I can easily tell the difference between the two. They've both been burned more than 50 hours. The BE's I got first so they have been burned in longer.
First, I will say that both headphones need a good seal to get the optimal sound from them. If it's not sealed and not positioned right, they both seem to "leak" the sound out, like the instruments are far away. They take longer to put in your ear just right than any IEM I've used (note that these are the most expensive IEMs I have for now and I guess a lot of top tier IEMs can be like this.) This sounds like first world problems and it is, but it's just as annoying as someone who has to change the channel on their TV instead of the remote.
The difference in the bass response is pretty big. Groups like Daft Punk will really show it. And because the bass is so powerful on the BE, it does recess the mids for me. So I see it as the BE is more consumer friendly for people who like that thump while the MKII being more neutral is for those who like things more musical. The other thing is because the BE bass is so powerful, it might be fatiguing since you feel your ears vibrate.