I have all three brands, GK, Vic Firth, EX-29.The vic firth SIH2 / Extreme isolation 25 or 29 / DT770M . These headphones, in this order, seems to offer 25 / 29 / 35 db of isolation. However after reading multiple threads, it seems that the 35db of isolation of the DT770M are actually not isolating as much as the 25db of SIH2. Not sure about the ex25/ex29, concerning isolation, some says it s better, other not, than the Vic firth.
I know a lot of people love the GK ultraphones, but these are out of my price range considering the shipping costs to my place.
The GK are by far the best sounding of the three, and the construction provides the best isolation of the three.
The Vic Firth models have better isolation than the EX-29, but don't sound great. IOW, you won't be evaluating your mix with these.
The EX-29 sound okay (not good enough to mix with, either), but their isolation for drums (percussive) doesn't seem very good. It's okay for guitars and singing, but the way it's constructed doesn't seem to attenuate percussive waves as well as the other two models.