Fulmination charge has passive int, which is really underestimated for some reason. I've been wearing an 895 twisting winds for a while now purely because it has 1875 int on it passive, the proc is just gravy. I'd freaking love a really high ilvl fulmination charge.
As far as mastery goes I'm fairly confident that its close enough with the other secondaries that it really doesn't matter, especially in any situations with more than 1 target where mastery typically becomes equal with the other stats. I'd personally never go out of my way to stack it, but I'm not going to sacrifice ilvls just because a piece has mastery on it.