DO NOT get the black gels.
If you want absolute isolation go with clear gels. They do get hot though...hotter than leather even. It's pretty brutal for some people.
I'm looking to buy custom MMX300's while BD has their 15% deal.
From my understanding they're DT770s with a mic but what I want to know is the different between the ear cup materials. I don't think I want velour because I want isolation but I'm not sure whether to get leather or gel pads. I've also heard that there's a different between the transparent gel and the black gel cup. Any insight on this?