Many hi-po pads dust enormously. There's been lots of discussion of this on the Miata board, and there doesn't seem to be a high performance pad that isn't dustier than stock. After a day on the track, my wheels are black. Mind you, some of that is bound to be due to the fact that 2 weekends of use will completely eat a set of pads. So, more pad material "dematerializing" in a fixed length of time.
I'm sure there's a Mustang board out there where you can find many opinions (informed and otherwise) that can help you choose.
Also, most brake dust washes off fairly easily when its fresh. After it has "baked on" for a while, not so much.