I imagine it's faster in dungeons if only because it's easier to jump into ilvl 70 battle content than ilvl 70 gathering content. In addition, the necessary low level mats can make things slower. That said, I've been working on GC achievements while SBing battle, crafting, and gathering sets. Crafting goes by the fastest with battle close behind (granted, this is level 49 GC leves, not dungeons), while gathering lags behind. This may be alleviated somewhat if I go after unspoiled nodes in my travels as well though.
